单项选择题

各种液压管液压后呈正六边形,其对边距S的允许最大值为()mm。 

A.S=0.8×0.993D+0.2;
B.S=0.8×0.993D+0.1;
C.S=0.866×0.993D+0.2;
D.S=0.866×0.993D