Question

If you write a sentence with an unclear antecedent, it means you used
A. an object pronoun instead of a possessive pronoun.
B. a plural pronoun when a singular pronoun was needed.
C. a possessive pronoun instead of a subject pronoun.
D. a pronoun that could refer to more than one person, place, or thing.

Answer 1

If you write a sentence with an unclear antecedent, it means you used a pronoun that could refer to more than one person, place, or thing. 
For example: I never go to that place because they have stale bread.
Who does they refer to? We don't know, it is unclear. 

Answer 2

The anser is D. a pronoun could refer to more than one person, place, or thing.