输送机巷，采区进、回风巷中的允许风流速度是（）m/s。
A.0.15～4
B.0.25～4
C.0.25～6
参考答案：C
The new stadium being built for the next Asian Games will be the present one.
A．as three times big as
B．three times as big as
C．as big as three times
D．as big three times as
凸透镜对光有 ______作用；把一个焦距5cm的凸透镜当放大镜使用时，物体到透镜的距离应 ______（选填“大于”、“小于”或“等于”）5cm．
