Introduction: Basically there are two teaching methods.
1. Lecture method:

The latter part of the 20th century has seen a continuous increase in economic growth, but such achievements, according to L.R. Brown, do not necessarily make up a cause for celebration. 点击查看答案

This essay is taken from the State of the World, a sourcebook published by the United Nations, which updates information each year on such world conditions as poverty, overpopulation, air and water quality and agricultural land. 点击查看答案