无内胎轮胎由（）、胎圈橡胶密封层和气门嘴组成。
A.外胎
B.内胎
C.气密层
D.垫带
参考答案：C
A．周期是0.2s
B．波长是0.5m
C．波速是2m/s
D．经1.6s传播了8m
– “Have you moved into the new flat?”
“Not yet. The room ________.”
has been painted B. is painted C. paints D. is being painted
