A.
Explanation.
A prepositional phrase is used as an adjective or adverb; that is, it modifies a noun or a verb. In the sentence “He left after lunch,” the prepositional phrase after lunch is used as an adverb to modify the verb left. It tells us when he left, as do “He left earlier” or “He left later.” There is no adverb in English that says, “He left post-lunch-ly.” It explains the cat [the subject of the sentance] is sitting on the mat – the preposition indicates that the cat is doing something to the mat. The cat is focalised because it is acting out the verb. The terminology "cat" would be a noun here. I haven't done this in a while, so it's kind of refreshing to me.
I tried pff. I'm not sure if it has helped, but I hope it did- if it didn't, I'm sorry .,.