重点讲解：
1. watch out
小心，提防（不愉快的事情或陷入困境）；
eg. I advised them to watch out for slick spots on the sidewalk.
我叫他们当心人行道上路滑的地方。
eg. You have to watch out for insincere people.
你得小心那些虚情假意的人。
2. scout for
（在某地）搜索，寻找；
eg. A team of four was sent to scout for a nuclear test site.
一个4人小分队被派出寻找核试验地。
eg. Go and scout for firewood for the picnic.
去找些柴来做野餐。
3. on purpose
特意地；故意地；有意地；
eg. He explained that he have not do it on purpose.
他解释他不是故意做这件事的。
eg. I don't think he stepped on your toes on purpose.
我想他不是有意伤害你的感情。
