The answer to your question would be that the sentence that has a misplaced modifier is the following one: In school, my mother encouraged me to join the band. That is, the correct option would be B.
A misplaced modifier is a word, phrase, or clause that is separated from the word it modifies/describes. Consequently, sentences with misplaced modifiers sound awkward and even confusing. In this case, the misplaced modifier makes it sound as if the speaker's mother was at school when giving him the piece of advice.
Answer: B. In school, my mother encouraged me to join the band.
The modifier in this case is misplaced as it makes it sound like the mother was at school when she gave the advice. Modifiers can be very important to the structure of a sentence as they can significantly change the meaning if misplaced.
All the other examples express the meaning of the sentence clearly.
