Question

which of the following contains a vague pronoun reference? after peter explained the chemistry homework to dave, peter understood it better, too. after peter explained the chemistry homework to dave, he understood it better, too.

Explanation:

In the second sentence, the pronoun "he" is ambiguous as it's unclear whether it refers to Peter or Dave. In the first sentence, "it" clearly refers to the chemistry homework and there's no pronoun - reference ambiguity for people.

Answer:

After Peter explained the chemistry homework to Dave, he understood it better, too.