The scientist corresponds with colleagues in order to learn about matters ________ to her own research.

Hefei is a beautiful city, isn’t it—Yes. There are about two ____ visitors here week.

No one is allowed ____ the room in the daytime..

I was doing my homework _______ a dog came in.

NASAhas made a ________ that our earth has no threat associated with the film 2012which is based on pure myths.