I regret _____ hard at school, or I would have succeeded in passing the exam.
The band was very successful in the seventies, most of _____ members were in their twenties.
---Did you enjoy yourself in Hefei this summer? ---________ It was too hot.
Every year _____ money are spent on environment protection.
It was her careless driving that _____the terrible accident.
Bill thought rain was out of question, so he didn’t bring umbrella.