Fill in the blank with the most appropriate option.
The horn of the car ahead was ________________ by the resistance of the thick air.

Correct option is D

The correct option to fill in the blank is (d) muffled.
"Muffled" means that the sound is muted or made quieter by something, in this case, the resistance of the thick air. The word appropriately fits the context of the sentence.
Meanings of other options:
Dim: Relates to light, not sound, so it’s incorrect here.
Faint: Could describe a weak sound, but doesn’t suggest the sound is being blocked or subdued by something.
Mute: Implies the sound is completely gone, which doesn’t match the context.