车辆在轨道上蛇形运动，是轨道方向不良引起的，这种运动产生的（）对轨道损坏严重。
A.垂直力
B.横向水平力
C.纵向水平力
D.纵向垂直力
参考答案：B
生物的生活离不开环境。你知道青蛙的冬眠和哪一种环境因素有关吗？ [ ]
A．温度
B．青蛙的天敌
C．阳光
D．与环境因素无关
看图完成答句，一空一词。
1. How many people can you see in the picture?
I can see two ______ and two ______.
2. Where are these people?
They are in the ______, because there is a ______ on the wall.
3. Where is the plant?
It's ______ the ______.
4. Who has straight long hair?
The second student ______ the ______.
5. Who wears a cap?
The ______ student standing ______ a girl.
