1.Be careful.The first step is broken.
2.In the late of 1970s great changes took place in China.
3.He said he had bought a 5-pound bag of oranges.
4.In the 1870s,when Marx was already in his fifties,he found it important to study the situation in Russia,so he began to learn Russian.
5.When she was in her teens Mary began to work.
6.Half of the land brlongs to the owner of the house ang the other land is the old man's.
7. There is a ten percent discount on everything in the store.
8.I am writing a composition.I've written fifty percent,that is the same as writing a half.
9.At the begining of the summer vacation he has finished two-thirds of his homework.
快快快!!!!!!