一个临时路障被放置在建筑工地周围以确保安全。

A temporary ___barrier was placed around the construction site to ensure safety.

只有授权人员才能用他们的钥匙打开这道闸门。

Only authorised personnel can open the ___barrier with their keys.

高高的屏障阻止了任何人非法穿越边境。

The high ___barrier prevented anyone from crossing the border illegally.