12. The main idea of the third paragraph (the highlighted portion) is that:

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

The third paragraph mainly introduces that in the mid-nineteenth century, various new inventions made possible the development of modern private letters. L41-44 are paragraph topic sentences. Item F is in line with the intent of the paragraph.

Item G: It is just a detail and cannot serve as the main idea of ​​the paragraph.

HJ item: There are no new inventions mentioned, but this paragraph focuses on introducing inventions.