單項(xiàng)選擇題先張法預(yù)應(yīng)力施工時,預(yù)應(yīng)力筋放張時混凝土強(qiáng)度應(yīng)不低于設(shè)計強(qiáng)度的()

A.50%
B.75%
C.90%
D.100%