My parents never remember my phone number, and they always have to look it up ________ they call me．

1. A.
   every time
2. B.
   for the time
3. C.
   at the time
4. D.
   in a time

 My parents never remember my phone number，and they always________ look it up every time they call me.

     A．can        B．must      C．should      D．have to