掌握化学用语是学好化学的重要基础之一。下列化学用语与对应含义相符的是( )
A:H2O2——过氧化氢
B:2H —— 2个氢元素
C:O2—— 2个氧原子
D:Na+1——钠离子
A. Are there any trees in it?
B. Because the air in the park is fresh and it is good for my health.
C. Do you often read books in the park?
D. There is a lake, a bridge and some small hills.
E. No, there aren't any flowers near the lake
Tem: What's in the central park(中央公园)?
Sarah: ____
Tom: ____
Sarah: Yes, there are.
Tom: Are there any flowers beside the lake?
Sarah: Yes, I do.
Tom: Why not in the library?
科学记数法表示的数是﹣3.14×104,这个数的原数为( )
冬天,教室若长时间不开门窗,很多同学会感到头晕,注意力不集中,这是因为教室里( )