先天性青光眼发病机制为（）。

A.眼轴短

B.大角膜

C.房角结构发育不全

D.房角窄

E.瞳孔阻滞

If laid out in______straight line,______human digestive tract would measure approximately thirty-foot long.

A．a...the
B．/...the
C．the.../
D．the...a