This document discusses the use of simple past and past progressive clauses in a single sentence. It provides examples of sentences containing two clauses, one in simple past and one in past progressive. The clause in past progressive expresses the first event that occurred. It also discusses sentences where both clauses are in simple past or past progressive. When the dependent clause comes first, a comma is used. While can be used with past progressive and when is often used with simple past, but native speakers may use when with both.