The correct answer is B. When Andrew was in high school, he told me that his uncle was a World War II veteran.
Step-by-step explanation:
In grammar a pronoun refers to a word including I, you, he, she, it, they and we that substitutes a noun, which is a word used to name some person or place, for example, the noun Peter can be substituted by the pronoun he or the word cat can be substituted by the pronoun it. On the other hand, a confusing pronoun occurs when there are two or more nouns that can be substituted by a pronoun and it is not clear which of the nouns is the pronoun substituting.
This occurs in the sentence "Andrew told me that his uncle was a World War II veteran when he was in high school" because it seems the pronoun he in "when he was in high school" refers to Andrew's uncle and not Andrew himself which is the one we supposed it in high school. Considering this, the best revision for this sentence is "When Andrew was in high school, he told me that his uncle was a World War II veteran" because it clarifies the pronoun "he" does not refer to the uncle but to Andrew which ends with the confusing pronoun of the first sentence.