下面关于最大屈光力说法正确的是()

A．和最小屈光力主子午线相互垂直者为顺规散光

B．和最小屈光力主子午线不相互垂直者为逆规散光

C．主子午线在90°±30°位置者为规则散光

D．主子午线在180°±30°位置者为不规则散光

E．主子午线在30°～60°位置者为斜向散光

A single fitting installed in a pipeline that either blanks off the pipe or allows a full flow passage of a liquid through the pipe is referred to as a（）.

A.blind flange

B.pivot coupling

C.quick-release coupling

D.spectacle flange