重点讲解：
1. guard against 提防；防范；
We must be on guard against hidden enemies.
我们必须警惕暗藏的敌人。
2. apply for 申请；请求；
I should apply for the post if I were you, I think you stand a good chance.
如果我是你的话，我一定去申请这个职位。我认为你大有希望。
3. interact with 相互交流；相互沟通；
I like to interact with others, so I have many friends.
我喜欢和别人交流，所以我有很多朋友。
4. account for （数量或比例上）占；
The minority nationalities account for six per cent of the population.
少数民族占人口的百分之六。