The answer would be "in particular", you labeled it "b" but you might've meant "c"...? Anyway it's "in particular" because that's where the sentence shifts from the main focus to an example that supports it.
Fall.
The sentence should look like:
He might play soccer this fall, or he might play decide to play football.
Answer: D
Explanation: "less" almost always qualifies as an adjective, because it's describing a noun, that being support, which is a thing/idea.
You would use it as an adverb if you were using it to describe or add more information to a verb. Ex. "I've been trying to work <em>less</em> on the weekends." Work is a verb, so less would qualify as an adverb here.
