第32题：简便运算
用简便方法计算下式的结果
80−(16+4)=A80-(16+4)=A80−(16+4)=A
13−(3+7)=B13-(3+7)=B13−(3+7)=B
(40+5)+55=C(40+5)+55=C(40+5)+55=C
法则11：分配律，a ⋅\cdot ⋅ (b+c) =a ⋅ \cdot ⋅ b + a ⋅ \cdot ⋅ c .
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