To answer this question, we need to understand the comparative form of the adjective "foggy."
Option A) "foggier" - This option is correct. The comparative form of "foggy" is "foggier." This option correctly compares the level of fog in the valleys to the hilltops.
Option B) "more foggier" - This option is incorrect. The comparative form of "foggy" is "foggier." Using "more" with "foggier" is redundant and unnecessary.
Option C) "foggy" - This option is incorrect. It does not compare the level of fog in the valleys to the hilltops.
Option D) "fog" - This option is incorrect. It does not describe the comparative level of fog in the valleys compared to the hilltops.
The correct answer is Option A) "foggier" because it correctly compares the level of fog in the valleys to the hilltops.