(2013·合肥模拟)—　　　　bargaining is so interesting?—Sometimes it is a test to see who can stand their ground for the longest.

____ important to learn English well.

It was about 600 years ago __________ the first clock was made.

In my opinion, all Mr Li ______ good to his students in his class at present. He is very strict with them in their studies.

It might have been John _____ bought a present for Mary yesterday.