A complex sentence has an independent clause(a simple sentence) joined by one or more dependent clauses. A complex sentence always has a subordinating conjunctions such as because, since, after, although, or when (and many others) or a relative pronoun such as that, who, or which.
1.When she submitted her project work, she forgot to attach the teacher the poster.
2.The teacher returned her project work after she noticed the poster missing.
3.The students are busy preparing because they have exams tomorrow.
4.After finishing the preparation , Tom and Tumesh went to play cricket.
5,.Tom and Tumesh went to play cricket after finishing the prepartion.
- When a complex sentence begins with a subordinator such as sentences 1 and 4, a comma is required at the end of the dependent clause.
- When the independent clause begins the sentence with subordinating conjunction in the middle as in sentences 2, 3, and 5, no comma is required.If a comma is placed before the subordinators in sentences 2, 3, and 5, it is wrong.
- Sentences 4 and 5 are the same except sentence 4 begins with the dependent clause which is followed by a comma, and sentence 5 begins with the independent clause which contains no comma.