为保证行车安全，在同一区间，同一时间内，不得使用两种（）。
参考答案：闭塞法
Many people are in the park. Some _____ under the tree, _____ are talking at thhee table. [ ]
A. are sitting, others
B. sit, others
C. are sitting, the other
D. sit, the others
成数再保险
