____________ David says sounds right to Helen. That’s why she has made up her mind not to leave him _____________ happens.

It made Mary’s parents excited         Mary entered the final in the tennis match.

_______caused the accident is still a complete mystery.

It makes no difference to him______ you stay here or go to Hong Kong.

It remains doubtful ______ immediate measures could be taken to prevent underground water pollution.

_____ the city’s public school system should be open to the children of migrant workers has become the focus of discussion.

______ in the regulations is that you _____ other people the password of your e-mail account.

___ in the regulations is that you ___ other people the password of your e-mail account．    
A．What is required; not tell              B As is required; shouldn't tell
C．It is required; not tell                D．It requires; shouldn't tell

Everyone knows that________ is dangerous to play with fire, but________ is difficult is to prevent children from playing with fire.

_______ excited her parents most was that he was admitted to his dream college.