Combining short sentences into longer sentences is the first mark of a more mature writer in secondary school. Many standardized writing tests ask a student to take two short sentences from a passage and combine them effectively into a longer compound or complex sentence. This lesson explains exactly how to do that. It includes examples and explanations on compound and complex sentences, including how to use semicolons. It also explains when to use a comma in these sentences, and when to leave it out. Several written practices are included. Key included.