CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0 - Database Android

I've experienced some error in my program. I'm trying to make quiz app using radiobutton. The question and answer option is obtained from database.

This is some part of my code:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    /* Get Intent Parameter */
    /* Open Database File */
    db_helper.openDataBase();
    db = db_helper.getReadableDatabase();


    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    this.setContentView(R.layout.activity_exercise_question);

    Qcontent = (TextView) findViewById(R.id.txtQuestion);
    Qnum = (TextView) findViewById(R.id.txtNumb);
    a = (RadioButton) findViewById(R.id.rbA);
    b = (RadioButton) findViewById(R.id.rbB);
    c = (RadioButton) findViewById(R.id.rbC);
    d = (RadioButton) findViewById(R.id.rbD);
    g = (RadioGroup) findViewById(R.id.rgOption);
    next = (Button) findViewById(R.id.btnNextQuestion);
    next.setBackgroundColor(Color.GREEN);

    //To handle event when button Next is clicked
    next.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            int radioButtonID = g.getCheckedRadioButtonId();
            View radioButton = g.findViewById(radioButtonID);
            int idx = g.indexOfChild(radioButton);
            if (opsys.getString(idx + 1).equals(opsys.getString(5))) {
                nilai = nilai + 1;
            }
            quiz();
        }
    });
    quiz();
}


public void finish() {
    next.setText("Finish");
    next.setBackgroundColor(Color.RED);
    next.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            int radioButtonID = g.getCheckedRadioButtonId();
            View radioButton = g.findViewById(radioButtonID);
            int idx = g.indexOfChild(radioButton);
            if (opsys.getString(idx + 1).equals(opsys.getString(5))) {
                score = score + 1;
            }
            ExerciseQuestion.this.finish();
            Intent showScore = new Intent(ExerciseQuestion.this, ExerciseScore.class);
            String achieveScore = String.valueOf(score);

            Bundle bundle = new Bundle();
            bundle.putString("AchieveScore", achieveScore);
            tampilNilai.putExtras(bundle);
            startActivity(showScore);
        }
    });
}

private void quiz() {
    question_numb = question_numb + 1;
    if (question_numb < 10) {
        Qnum.setText("  " + Integer.toString(question_numb) + '.');
    } else Qnum.setText(Integer.toString(question_numb) + '.');

    checkResult();

    Qcontent.setText(opsys.getString(0)); //this is to set the question I've taken from db to TextView
    a.setText(opsys.getString(1)); //this is to set the option A I've taken from db to radiobutton
    b.setText(opsys.getString(2)); //this is to set the option B I've taken from db to radiobutton
    c.setText(opsys.getString(3)); //this is to set the option C I've taken from db to radiobutton
    d.setText(opsys.getString(4)); //this is to set the option D I've taken from db to radiobutton

    //To handle when question number is 10
    if (question_numb == 10) {
        finish();
    }
}

private boolean checkResult() {
    // TODO Auto-generated method stub
    int random10 = generateRandomNumber(10); //I've a method to generate Random number using Math.random() without repetition
    int random18 = generateRandomNumber(18);
    String query;

    Bundle bundle = getIntent().getExtras();
    int chooseContent = bundle.getInt("chooseContent");

    if (chooseContent == 0) {
        query = "SELECT question, a, b, c, d, answer FROM tbl_Exercise WHERE (id_topic=" + random18 + " and id_question=" + random10 + ")";
    } else {
        query = "SELECT question, a, b, c, d, answer FROM tbl_Exercise WHERE (id_topic=" + chooseContent + " and id_question=" + random10 + ")";
    }

    opsys = db.rawQuery(query, null);
    if (opsys != null && opsys.moveToFirst()) {
        return true;
    }
    opsys.close();
    return false;
}

Sometimes when I touch the Next button, the app crashes (but sometimes it doesn't, and it works like charm). The logcat is as follows:

06-04 19:14:16.884  10062-10062/com.coder.learningmodule E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.coder.learningmodule, PID: 10062
android.database.CursorIndexOutOfBoundsException: Index 0 requested, with a size of 0
        at android.database.AbstractCursor.checkPosition(AbstractCursor.java:426)
        at android.database.AbstractWindowedCursor.checkPosition(AbstractWindowedCursor.java:136)
        at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:50)
        at com.coder.learningmodule.ExerciseQuestion.quiz(ExerciseQuestion.java:106)
        at com.coder.learningmodule.ExerciseQuestion.access$300(ExerciseQuestion.java:19)
        at com.coder.learningmodule.ExerciseQuestion$1.onClick(ExerciseQuestion.java:68)
        at android.view.View.performClick(View.java:4443)
        at android.view.View$PerformClick.run(View.java:18442)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5021)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
        at dalvik.system.NativeStart.main(Native Method)

The error refers to Qcontent.setText(opsys.getString(0)); in quiz() method

After I read some related question in Stackoverflow, I have tried the following code, but it does not solve the problem

    opsys = db.rawQuery(query, null);
    if (opsys != null && opsys.moveToFirst()) {
        return true;
    }
    opsys.close();
    return false;           

I would really appreciate help and/or suggestion from anyone to solve this problem. Thank you very much.