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若a=cos5θ-cos3θsin2θ+cosθsin4θ,b=cos4θsinθ-cos2θsin3θ+sin5θ,
则复数a+bi等于
A.cos5θ+isin5θ B.cos5θ-isin5θ
C.sin5θ+icos5θ D.sin5θ-icos5θ