We'll learn much from this failure, so our suffering and efforts are not .
A. in return
B. in vain
C. at random
D. at all costs
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A. in return
(答案→)B. in vain
C. at random
D. at all costs
解析：B 考察介词短语辨析。In return作为回报；in vain白费地，徒劳地；at random任意地，随便地；at all costs不惜任何代价的。句义：完美将从这次失败中学到很多，因此完美所忍受的痛苦和付出的努力没有白费。故B正确。