清扫平台只起到缓冲和阻截上部台阶滑落的岩石的作用。
参考答案：错
A big bush fire ___ in Australia last night, but fortunately everyone ____escape. [ ]
A. took place; could
B. happened; can
C. broke out; was able to
D. happened; could
三角函数Cos60°的值是：（）
A、0.5
B、0.707
C、1
D、1.414
