13. The main idea of the second paragraph (the highlighted sentence) is that:

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

Item D: The topic sentence is the last sentence, we cannot lose the taxonomy because it is so important to our understanding of the world.

Item A: There is no mention of the decline in the number of experts.

Item B: No mention of natural history.

Item C: "Classification is not an obscure science because it is widely studied", the error is because the focus of this paragraph is not whether it is difficult to understand, but to emphasize that classification is very important.