I often the words I don’t know in the dictionary or on the Internet.
In the experiment you should keep a watchful eye ______ the developments and record every detail.
He said ______ couldn’t he work out the problem but his teacher didn’t know how to do it.
The problem ______ many children,especially girls,have ______ school is getting more and more serious.
Usually children are allowed to ______ when they are six years old.
–Did you take enough money with you? –No, I needed _______ I thought I would.