Past simple or past perfect?

By the time we ____, everyone had left.

• arrived

• had arrived

I _____ a long time ago.

• finished

• had finished

• Either could be used here.

By that time, everybody ____ exhausted.

• was

• had been

• Either could be used here.

She told me she ____ it ages ago.

• did

• had done

• Either could be used here.

I ____ of it until you mentioned it.

• didn't hear

• hadn't heard

I ____ enough time to finish the exam.

• didn't have

• hadn't had

• Either could be used here

If I ____, I'd have helped.

• knew

• had known

• Either could be used here

If I ____, I'd tell you.

• knew

• had known

• Either could be used here.

No sooner ____ than I realised what was going on.

• did I arrive

• had I arrived

• Either could be used here.

Until last month, I _____ it before.

• didn't try

• hadn't tried