The italicized word OVER can be used either as a preposition or as an adverb in a sentence. In this particular sentence, the correct answer is adverb.
When over is used as an adverb, it is not followed by any word which would create a phrase along with it (as is the case here). Compare OVER as a preposition (A bird flew over the lake - we can see over what) and OVER as an adverb (Could you come over - we don't know over where or what).
Less is a comparative form of adjective. Comparative degree of comparison is comparing two nouns. In the sentence, the space in the old house is compared to the new ones, Positive degree is used in describing only one noun, and superlative degree compares three nouns.
B). Categorize A Topic
I believe this is the answer, if I am wrong, somebody feel free to correct me. :)
