Although everything seems to have been taken into consideration，       accident can happen when the astronauts walk in            space．

A．不填；the

B．an；the

C．the；the

D．an；不填

一般情况下，太阳病的自然病程约是（）。

A.一二天

B.三四天

C.六七天

D.十一二天

E.以上皆不是