중3 천재교육 영어 교과서 문장 질문

다음 중 잘못된 문장을 찾는 문제예요.
a. Jiho is sleeping with a pen in his hand.
b. She is talking as if she were a baby.
c. They will spend money on building both a shopping center and a library.
d. Could you tell me whether John passed the exam?
e. One of the players is wearing a yellow cap.
앞서 b가 틀렸다는 답변을 봤는데, 구체적으로 설명 부탁드려요.