水中氢元素的质量分数为( )
A.5.6%
B.9.9%
C.11.1%
D.12.1%
答案:C
Be careful when you go ____ the street because the traffic
is very busy at the moment.
A.across
B.behind
C.between
D.over
下图为某中学独轮车比赛的瞬间实景拍摄,时间为夏季15点。图中直线跑道的走向大致是()
A.东北一西南
B.东西
C.西北一东南
D.南北