For example, in the demonstration section on smoking, the central idea is "health problems caused by smoking" and the key word is "health problems".

2. Summarize the details and answer the questions implied in the topic sentence.

In the demonstration paragraph about "smoking", the implicit question is "What are the health problems caused by smoking?" The answer given in the conclusion sentence is that it is considered as one of the main causes of death in our society.

3. Use different words to express the same central idea

In the demonstration paragraph about smoking, the key word in the topic sentence is "health problem", while in the conclusion sentence, the key word is "cause of death".