With his brows knitted, the surgeon contemplated the difficult operation he had to perform.
【正确答案】 D
【答案解析】解析：contemplate“沉思，打算”；succeed in“成功于”；decide against“决定不做某事”；go on with“继续做某事”；think deeply about“深思”。根据句意，医生应该是就这个有难度的手术方案进行考虑。故选D。