24. The main purpose of the fourth paragraph (the highlighted portion) is to make clear that the glass used to build walls today has to be:

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

The topic sentence of the fourth paragraph is L55-56, the current glass is more efficient and safer than the previous glass. Item H fits the purpose of the paragraph.

FGJ Item: It's just a detail, it can't serve as the main point of the paragraph.