Choosing to visit the Shanghai Expo on a late afternoon can make you see two to three times as many of the most popular pavilions between 6 pm and closing time ____ you hurry.

A．when

B．unless

C．where

D．if

我国社会主义医德原则确立的时间是（）

A.1949年

B.1956年

C.1981年

D.1991年