已知圆锥的表面积为，且它的侧面展开图是一个半圆，则圆锥的底面半径为
—Where are my English books? —Look!They are just your hands.A.in B.at C.of
— is Yang Liwei from ? —He’s from Liaoning.A.Where B.When C.Why
—Happy birthday you,Daming ! —Thank you.A.to B.with C.at
—Who can help ? —Sorry,I can’t.A.me B.I C.he
—What are the birds doing ? —They are in the tree.A.sing B.singing C.sings
，且它的侧面展开图是一个半圆，则圆锥的底面半径为
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