1. catch fire the house caught fire when they were away. 在他们外出时房子着火了。She was standing to close to the fireplace and her dress caught fire. 她站得离壁炉太近了，衣服烧着了。
2. on fire on fire / catch fire 都是“着火”的意思，不过catch fire强调动作，on fire强调状态，如：Look! The house is on fire.
3. look out Look out！（当心、小心），比Take care! 或Be careful! 语气要强，往往用于某种紧急情况或可能出现危险的场合。Look out! There’s danger in the forest. 后还可接for短语：Look out for the rock in the water. 当心水里的石头。
