In the experiment we kept a watchful eye （ ） the developments and recorded every detail.

Scientists say it may be five or six years （ ） this medicine is tested on human beings.

_____, the professor is still trying to learn a new language.

When I was a child, I used （ ） to the river and bathe in the evening.

I think it’s high time we _____ strict measures to stop pollution.

The hotel couldn’t offer （ ） for all four of us.

（ ） weather may be too hot to the tourists.

I’m trying to be more （ ） when I go shopping, and only buying what I really need.

I certainly didn’t appreciate （ ） when I made mistakes.

（ ） when she started complaining.

He （ ） me to give up the holidays in Spain next month.

He had never given a speech to so many people, so he felt（ ） .