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       puzzle, bewilder, perplex, baffle

　　key crucial, critical

　　conserve, preserve

　　change, alter, modify convert into,

　　allege, assert, declare, claim

　　happen, occur, take place

　　deny, negate

　　appraise, assess, evaluate, estimate

　　attribute, ascribe, credit, impute,

　　reason, factor, cause

　　development, advance ,progress

　　important, critical, essential

　　rule, regulation

　　supply, provide, afford

　　assure, ensure, guarantee, pledge,

　　often, frequent, constant

　　express, voice, utter, pronounce

　　cost, expense, expenditure

　　buy, purchase

　　encourage, embolden, hearten, inspire

　　abundant, copious, profuse, ample

　　bad, baneful, evil, harmful, detrimental

　　useful, helpful, beneficial, profitable, rewarding

　　result in, bring about, give rise to, lead to, cause