3. The main idea of the sixth paragraph (the highlighted portion) is that:

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

The main content of the sixth paragraph is: the position of Jacob's Mound is between heaven and earth (you're not up in the sky and you're not on the ground; you're nicely in-between...). Comparison of option B It is confusing, the original text does mention fresh air, but this is a detail, not the gist, and the fresh air is also to illustrate the special location of Jacob's Mound;