It was about 600 years ago ______the first clock with a face and an hour hand was made .
Thousands of athletes _______ in many countries competed ______ medals in the 2008 Olympic Games in Beijing.
The Science Museum, _______ we visited during a recent trip to Britain, is one of London’s tourist attractions.
The problem is _________ we can finish the work in time.
A monument was set up at the centre of Tian’men Square ______ those who devoted their lives to our country.
-What do you think of Peter? -He is a helpful person. He is always helping people without expecting anything_______.