Read the whole paragraph and know what it is about. What do you mean by main?

As for the meaning of this passage, my suggestion is: read the whole paragraph twice first. Understand its meaning with your heart, and don't wander repeatedly in one or two sentences (if you don't know this sentence very well, for example, you don't know the two words in this sentence, and so on). ). You should understand it with your heart, yes, and know the overall meaning of this passage by the author. Then there are two ways: 1 summarize the central meaning of this passage by yourself, which is the core point of the author's paragraph. See which sentence in the paragraph best fits your summary and choose it as this argument. 2 common skills, read the two sentences at the beginning and end of the paragraph twice to see if it is appropriate to summarize the meaning of the whole paragraph. If so, this sentence is an argument. If you can't, or there are more sentences in the paragraph that can summarize the whole meaning, think again. It's just that arguments usually appear at the beginning or end of a paragraph with a higher probability.