It is estimated the project will last four years.

　　據估計，這項工程將持續(xù)四年。

　　The child disappeared from his home some time after four.

　　這孩子四點多的時候就離家不見了。

　　She asked her students to get into groups of four.

　　她讓學生每四人分為一小組。

　　First get students to form groups of four.

　　首先讓學生分成四人一組。

　　Students come here from the four corners of the world.

　　學生從世界各地來到這里。