A.External noise.B.Physiological noise.C.The effect of a cold.D.Psychological effect.

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A.External noise.

B.Physiological noise.

C.The effect of a cold.

D.Psychological effect.

请帮忙给出正确答案和分析,谢谢!

热搜:a是b的充分条件,b是a的必要条件吗