But Abou-Zahr hastens to add that countries in Africa do not present a uniformly bleak picture.

VOA: standard.2009.05.21

So let's picture what this looks like here, and we'll start with four and we'll add in our last two.

让我们想象一下它的样子，我们先给出四个，然后加上另外两个。

麻省理工公开课 - 化学原理课程节选