Explain what is wrong with the following sentence: She decided to evaluate the program, which would take five months.

The relative clause is not clear.

Explanation:

A relative clause is used to define or describe or identify the noun that it is before. However, in the first clause of the sentence (She decided to evaluate the program) there are two things (a noun and a verb) that can be described (which is used to do so, for a person, who or that are necessary; ) however, the second part (which would take five months) could refer both to the program or to the evaluation, so the meaning is not completely clear.