Substances will expand or contract ______ heated or cooled, but this is not the case with water.

1. A.
   when they will be
2. B.
   if they will be
3. C.
   as they being
4. D.
   when

Substances will expand or contract ______ heated or cooled, but this is not the case with water.

A. when they will be                         B. if they will be 

C. as they being                                 D. when