为确保参加活动人群安全，一定要设置具有隔离模型飞行区和人员活动区的标志线也就是安全线。
参考答案：对
________ seems to be a strong competition in China for senior high students to enter college or university.
A．It
B．This
C．That
D．There
广义表是线性表的推广，是由零个或多个单元素或______所组成的有限序列。
