Answer & Explanation
C) The girl, whom you have met yesterday is my sister
Here in the given options, The girl, whom you have met yesterday is my sister is the sentence which has relative pronoun.
The pronoun which is used to connect a clause or phrase to a noun or pronoun is called as relative pronoun.
The most common relative pronouns are who, whom, whose, which, and that. Sometimes when and where can also be used as relative pronouns.