In each set of sentences, choose the sentence that has a problem with pronoun-antecedent agreement. Students sometimes discover they don't like their chosen field.
A student sometimes discovers he or she doesn't like their chosen field.
Students may lose interest in their chosen field.

The sentence in this set of sentences that has a problem with the pronoun-antecedent agreement is:

A student sometimes discovers he or she doesn't like their chosen field.

Explanation:

The pronouns are "he or she" and "their."  These pronouns are preceded by the noun "student."  A better construction of the sentence is the first one, which says: "Students sometimes discover they don't like their chosen field."  The third sentence is also well-constructed.  They are simpler and less complicated than the second sentence.  Again, the first sentence has perfect agreement between the noun "students" and the pronouns "they" and "their."

explanation:

the silver bells of the sleds are merry and keep time in the winter nights while the sky twinkles happily. the golden bells of weddings are delightful in their peaceful happiness, foretelling a rapturous future. meanwhile, the brazen alarm bells scream frightfully in the night, with a discordant and desperate sound. in their clamor, these bells convey terror, horror, and anger. finally, the iron bells are solemn and melancholy, while those in the church steeple are like ghouls who feel happiness. the king of the ghouls, who rings the bells, cheerfully keeps time with the moaning and groaning bells.