2.a (different from …, fixed collocation)

3.c (going on a diet means dieting, fixed collocation)

4.c(waiting has been in line for 1.5 hours, which can be regarded as Tom has waited ... now perfect ...)

5.a (it's about time, followed by the simple present tense)

6.d (lost contact)

7.d (being introduced, Remembering sth means remembering to do something, here is passive, so the passive voice is used).

8.c (sharing here means how many people share a bedroom)

9.d (high efficiency)

I hope you can be satisfied with the explanation, and I wish you a smooth study!