Explain the four structures of sentences?

1. Simple Sentence: A simple sentence consists of a single independent clause, which contains a subject and a predicate. It expresses a complete thought and can stand alone as a sentence. For example, "The dog barked."

2. Compound Sentence: A compound sentence consists of two or more independent clauses joined together by coordinating conjunctions, such as "and," "but," or "or." Each clause in a compound sentence can stand alone as a separate sentence. For example, "The cat meowed, and the dog barked."

3. Complex Sentence: A complex sentence consists of one independent clause and one or more dependent clauses. A dependent clause cannot stand alone as a sentence and is usually introduced by subordinating conjunctions, such as "because," "although," or "while." For example, "I went to the store because I needed to buy some groceries."

4. Compound-Complex Sentence: A compound-complex sentence consists of two or more independent clauses and one or more dependent clauses. It combines the features of both compound and complex sentences. For example, "I went to the store because I needed to buy some groceries, and I also picked up some milk on the way home."