Nobody knows for sure why and how dinosaurs disappeared from the earth in such a short time.

没有人确切地知道恐龙为什么、又是怎样在这么短的时间内从地球上消失的。

He arrived at the cinema early to <b>make sure of</b> a seat.

为确保有座位，他早早地到了电影院。

We <b>make sure</b> (<b>that</b>) we take good care of students on campus.

我们确保在校园里照顾好学生。

She’s not perfect, to be sure, but she is pretty.

她固然不是十全十美，但很漂亮。