Answer:
C: A compound sentence is two independent clauses joined by a colon.
Step-by-step explanation:
Note: There may still be many compound sentences which are without colons. and there may be compound sentences with more than two independent clauses as well.
Compound Sentences:
A compound sentence has at least two independent clauses.
Examples:
1: Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. (Albert Einstein, 1879-1955)
2: Any fool can criticize, condemn, and complain - and most fools do. (Dale Carnegie)