He is good at maths and it won’t be long ____ he works out the problem.

He is good at maths and it won’t be long ____ he works out the problem.

1. A.
   since
2. B.
   until
3. C.
   before
4. D.
   when

He is good at maths and it won’t be long ____ he works out the problem.

   A. since           B. until               C. before        D. when

He is good at maths and it won’t be long ____ he works out the problem.