单选题 He had tried to ______ sleep by all his usual methods, but with no success.

【正确答案】 B
【答案解析】(induce引起，导致)。句意为：他想尽各种常见的办法催眠，但均未成功。 A．secure保证，获得；C．impact对……产生不良影响；D．infer推断。