after the rain ended, the sky became blue --is this a complex sentence?
Yes.
Yes, the sentence "After the rain ended, the sky became blue" is a complex sentence. A complex sentence consists of an independent clause (a clause that can stand alone as a sentence) and one or more dependent clauses (clauses that cannot stand alone as a sentence).
In this case, the independent clause is "the sky became blue," which can be a complete sentence on its own. The dependent clause is "after the rain ended," which cannot function as a standalone sentence but adds additional information to the main clause.