Final answer:
A simple sentence has one main clause, while a compound sentence has two or more main clauses joined by a coordinating conjunction. A complex sentence has one main clause and one or more subordinate clauses. Finally, a compound-complex sentence contains two or more main clauses and one or more subordinate clauses.
Step-by-step explanation:
A simple sentence has one idea expressed in a single main clause (also known as an independent clause). A main clause contains a subject and a predicate and can stand alone as a sentence. A simple sentence can be short or long, as shown in the examples below. The phrases in the long sentence add information, but the sentence remains a simple sentence nonetheless because it has only one clause.
The coronavirus spread around the world in 2020.
School-age children and college students were pushed into virtual learning environments in March 2020, with schools closing for unspecified lengths of time.
A compound sentence contains two or more main clauses that are equally important to the meaning of the sentence. To create a compound sentence, you can use a coordinating conjunction (for, and, nor, but, or, yet, so) to join the main clauses. Remember the mnemonic device 'fanboys' to recall the coordinating conjunctions.
A complex sentence contains one main clause and one or more subordinate clauses. The subordinate clause (also known as a dependent clause) cannot stand alone as a complete sentence and relies on the main clause to make sense.
A compound-complex sentence contains two or more main clauses and one or more subordinate clauses.