例句：
Be sure to give your family my regards.
务必代我向你的家人问好。
Even if you did see someone, you can't be sure it was him.
即使你确实看见有个人，也不能保证那就是他。
England must win this game to be sure of qualifying.
英格兰队必须拿下这场比赛才能确保获得资格。
He is intelligent, to be sure, but he's also very lazy.
他固然聪明，但也很懒。
Whether or not we're successful, we can be sure that we did our best.
不管成功与否，我们确已尽了最大努力。