challenge/'tʃælɪnʤ/

n. sth that needs great effort and ability

v. say or show that sth may not be true, correct or legal

n. [C; U] 挑战（性）：face/accept a challenge 面对/接受挑战

◇[challenge of (doing) sth] meet the challenge of the new century 迎接新世纪的挑战

v. [T] 挑战：He is bold enough to challenge the authority of the boss. 他胆子够大，敢挑战老板的权威。