Which of these is a pronoun? A. they B. who C. that D. thiers.

Pronoun is a word that can replace a noun, for example: I, you, he, she, we.

For example, instead of saying, The teacher talked, you can say "She talked"

"They" is a pronoun because it can replace a noun such as the teachers.

Instead of saying The teachers talked, you can say "They talked."

"Who" is also a pronoun as it can act as a subject.

You can say: "Who is this man?" and who is a pronoun (specifically interrogative pronoun).