Answer:
A. Startled by its own reflection, the cat jumped in the air.
Step-by-step explanation:
Identifying key parts of sentences and sentence structure is crucial throughout English.
You should remember that a pronoun is simply something that can really replace a noun. It's quite often these are confused with nouns, and that's rightfully so because they are quite similar.
POSSESSIVE pronouns, on the other hand, take these noun-alikes and add possession to it. They are NOT to be confused with the subject of the sentece, however, they show some form of possession TO that subject.
A. Startled by its own reflection, the cat jumped into the air.
Notice how "its" is defining something belonging to the cat, not the cat itself.
B. After Sarah mowed the grass, she left for the game.
There is no possessive pronoun here. "She" is but a mere pronoun, the subject. You cannot confuse this for showing possession because one cannot simply possess themselves, that's just. . .wrong. And odd. And will never be spoken of again :). Starting AFTER I finish with the other two!! What "she" is, is actually a SUBJECT pronoun! Who would've guessed??
C. Has anyone seen the movie The Miracle Worker?
. . . I don't even see a pronoun in this sentence, however, the hypothetical "subjects" in this case is referred to via "anyone," which might trick some into thinking it's a pronoun, so I suppose it's necessary to point out that neither is anyone showing any form of posession to anything, but anyone is far too vaugue of a term.
D. Kevin is the friend who helped me build the treehouse.
There is ALSO not a possessive pronoun present here, however, there IS an object pronoun, "me." Me isn't defining the subject because the subject is Kevin, thus making "me" define a secondary "object" (so to speak) within the sentence, thus making it an OBJECT pronoun. There is nothing in this sentence showing possession though!!
A is your only shot.