This sentence has one independent clause:
The lantern flickered in the tunnel.
What is a simple sentence.
This sentence contains two independent clauses joined by a conjunction:
The boy hesitated, but he stepped into the glowing doorway.
What is a compound sentence.
No one thought the Wright brothers' flying machine would work but that didn't stop them.
No one thought the Wright brothers' flying machine would work, but that didn't stop them.
This sentence includes one independent clause and one dependent clause:
Although the air grew colder, the travelers continued deeper underground.
What is a complex sentence.
The population of Jonesboro is about 65500.
65,000
This sentence uses two independent clauses and at least one dependent clause:
When the crystal began to hum, the walls trembled, and the children grabbed each other’s hands.
What is a compound-complex sentence.
This sentence type appears when a writer blends multiple ideas, using both coordination and subordination:
The tunnel widened as they walked, and they gasped when the underground city came into view.
What is a compound-complex sentence.