These pictures show young readers what led Darwin to form his great discovery: the evolution of species through natural selection.

VOA: special.2009.02.27

Groups were assigned and the students came from all over the world, so we made great efforts in the selection of the student groups that we put together.

对来自世界各地的学生,进行分组，我们花了很大力气选择,放在一起的组。

麻省理工公开课 - 媒体、教育、市场课程节选