安全网的系绳和边绳的截面积，至少为网绳截面积的()。
A.1倍
B.2倍
C.0.3倍
D.3倍
参考答案：B
Yellow Mountain is such an attractive place of interest ________ everyone likes to visit. [ ]
A. as
B. that
C. which
D. what
堆排序是一种______排序。
A．插入
B．选择
C．交换
D．归并
