Question

It rained heavily, so we _______ stay at home watching TV or surfing the Internet all day

1. A.
   could
2. B.
   had to
3. C.
   must

Answer 1

B
天气下着大雨，所以只能呆在家里看电视或上网，表示的客观的原因，have to表示客观的原因，意思为不得不，必须，故本题选B。