采用热风采暖和空气调节的车间,其新风口应设置在空气清洁区,新鲜空气的补充量应达到_m3/h•人的标准规定。
A.20
B.30
C.40
D.50
参考答案:B
I always take a bus to school, and I ______ ride a bike.
[ ]
A. always
B. usually
C. often
D. never
根据图中所给A、B两物体s﹣t图象,判断对应的v﹣t图象那个是正确的( )
A. B.
C. D.