It usually takes courage to an invitation.A. turn downB. turn upC. turn outD. turn to

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(答案→)A. turn down
B. turn up
C. turn out
D. turn to
解析： 词义辨析。turn down关小，调低，拒绝；turn up出现，露面，调高；turn out       结果是，证明是；turn to转向，求助于。句意：拒绝邀请通常需要勇气。所以选A。