Ballet is highly technical and it      professional dancers years to train.

A good teacher must ______ to his students the importance of a proper learning method.

Mr. Black must be worried about something, you can ______ it from the look on his face.

 The book isn't intended for general readers probably because the author _______ too many scientific terms(术语) in it.

Ted is such a helpful colleague that he is willing to do,       ,any favour we might ask him.