to be sure

的确, 诚然, 当然, 毫无疑问

例句与用法：

Book early if you want to be sure of a seat.

要想十拿九稳有个座位，那就早订座。

He is clever, to be sure, but not very hard-working.

他聪明是聪明，但是不怎么勤奋。

I left a message so as to be sure of contacting her.

我留下了张条子以便与她取得联系。

To be sure, he is young, but he is very experienced.

他确实很年轻，但他很有经验。

He likes to be sure of his bodily comforts.

他注重身体上的舒适。

Joan's not pretty, to be sure, but she's very intelligent.

当然，琼并不漂亮，可她非常聪明。