A singular pronoun is a noun that is only about 1 person
Therefore you would see that answer choices A B and C would be eliminated
A is NOT the correct answer because it's talking about more than one person, and that's plural.
B is NOT the correct answer because woman names something, but doesn't substitute a noun.
C is NOT the correct answer because it's talking about more than one person, and that's also plural.
D). She would be your answer because it's singular (talking about one person), and a pronoun.