An expert was _____ to give a speech on how to learn English well.

One of the collectors collected some seeds from a tree that had _____ him.

To make the students understand the problem the teacher tried to explain it, but the explanation just did not _________to the class．

The book is very valuable to us. That is to say, The book is of________.

 Children who ______ well will be given a red flower and an apple as encouragement.