单选题 I______him that I would help him if he had any difficulty in carrying out the task.
【正确答案】 B
【答案解析】解析：本题考查近义词辨析。ensure常用从句充当宾语，assure sb．that的意思是“跟某人保证……”，guarantee“保证”，常用做保证产品的质量，vow“宣誓”。因此本题正确答案为B。