preposition, or a verb with adverb and p reposition.

Most of the verb phrase idioms are nearly synonymous with loan words of Roman origin. In contemporary English, verb phrase idioms are preferred to corresponding single verbs of Romanic origin. Besides, verb phrase idioms can form noun compounds. Phrase verbs are usually more lively and expressive than single verbs. （详情参考书本P194~P195所有内容）

4. What are the points that we must pay attention to in order to use idiomatic expressions appropriately?

I think that non-native students should pay attention to the syntactic(句法的，语法的，合成的), structural and stylistic（风格的） analysis of idioms so that the non-native student can learn to use them appropriately. （详情参考书本P201最后一段）