I often get up ______ seven o'clock.
A. at
B. in
C. on
答案:A
如下图表示的是近视眼成像示意图,矫正近视眼应佩戴眼镜的镜片是________透镜(选填“凸”或“凹”)
电解水得到氢气和氧气的质量比为( )
A.4:8
B.1:8
C.2:1
D.1:16