All of the following sentences are compound EXCEPT:
C. Rice is the most widely-consumed staple food, especially in Asia and the West Indies.
A compound sentence has at least two independent clauses that have related ideas. The independent clauses can be joined by a coordinating conjunction (for, and, nor, but, or, yet, so) or by a semicolon, as you can see in the compound sentence examples below.
In either case, each half of the sentence must be able to stand on its own as a complete sentence. That means each half needs a subject and a verb. Checking if the different 'parts' of a sentence can be considered by themselves as a complete, autonomous sentence is the way to identify a compound sentence.
In this particular sentence, you only have one independent clause (only one complete sentence): "Rice is the most widely-consumed staple food". The remaining part of the sentence, "especially in Asia and the West Indies", is not a complete sentence as it doesn´t have a subject nor a verb; it depends on the "Rice is the most widely-consumed staple food".
