What to Write after a Topic Sentence

The writing task of Meow-meow Practice Exam 22 required students to write on "How to Get Rid of Depression," with "Everyone gets depressed once in while." as the topic sentence of the 1st paragraph, and "Whenever I feel down, I like to..." as the beginning of the 2nd paragraph. 

Reading the essays my students handed in, I found students didn't have problems with the 2nd paragraph.  However, many of them needed to rewrite the 1st paragraph because they failed to develop the topic sentence; instead, they wrote something new.   They wrote immediately after the topic sentence about how people got rid of depression.  If they had remembered what a topic sentence was there for, they would have not made this mistake.  In fact, I've mentioned the topic-supporting concept many times in class and gave examples too.   However, the interference from the first language seems too strong to avoid.

This afternoon after class, I asked Jack (莊子賢) in Class 310 to tell me what one should write after the topic sentence to support it so that his readers, after reading the supporting sentences, would say, "You're right.  Everyone gets depressed once in a while," he answered that one should write about under what circumstances people feel depressed.  Bingo!   That is the basic structure of an English paragraph.