在。。。中 / 在。。。下 / 在。。。上
As I understand them, they are used very similar to how you use them in English.

在．．．中 is like "during", "in the middle of", or just "in"

在．．．下 is like "under" ("Under the rule of...", "Under the stress of...", "Under the efforts of China and India...")

在．．．上 is like "on the..." ("On the merits of...", "On the basis of...")