It is estimated the project will last four years.
据估计，这项工程将持续四年。
The child disappeared from his home some time after four.
这孩子四点多的时候就离家不见了。
She asked her students to get into groups of four.
她让学生每四人分为一小组。
First get students to form groups of four.
首先让学生分成四人一组。
Students come here from the four corners of the world.
学生从世界各地来到这里。