Add values in a row, substituing 0 for NULL

I have a table that looks like this:

ID | VALUE A | VALUE B
----------------------
1  | 20      | NULL   
2  | NULL    | 100    
3  | NULL    | NULL   
4  | 100     | 50    

I want to run a query (Sqlite) that returns the ID and the sum of VALUE A and VALUE B (NULL should be zero). The result should look like:

ID | SCORE
----------
1  | 20
2  | 100
3  | 0
4  | 150