What are the comparative sentences in Questioning and Learning?

1. Academic research must have the spirit of doubt (or "scholars must have the spirit of doubt first": or "learning needs the spirit of doubt").

2. Lead out the central argument, stimulate readers' interest in reading, and demonstrate the central argument as an argument.

3. Through examples and comparative argumentation, the sub-argument that doubt is the basic condition for establishing new theories and inspiring new inventions in a positive way is clearly demonstrated, thus demonstrating the central argument.

In fact, the author expounds the function of "doubt" from both negative and positive aspects, and makes a clear summary in the middle of the article (section VI). This is not only the clarification and concretization of Cheng and Zhang's theory, but also the author's experience.