1·It consists of a main clause and one or more subordinate clauses. The subordinate clause is either a noun clause, an adjective clause or an adverb clause.
复合句有一主句，和一句或以上的属从子句。子句可以是名词子句、形容词子句或副词子句。
2·Put a secondary idea in a dependent adverb clause if you want to express an idea of time, place, cause or reason, purpose or result, concession or contrast.
在表达关于时间、地点、原因、目的或结果、让步或转折等内容的时候，把它们都放在副词从句位置。
3·It usually uses the modal element such as modal auxiliary, modal adverb and clause formally.
其表达往往是在句子中加入情态动词、情态副词和小句等情态成分。