Answer:
Grapefruits, in addition to lemons and oranges, are citrus fruits.
Step-by-step explanation:
All of these may work to some extent, but on account that this sentence is the only one that sounds completely right, I believe the last choice is correct.
Sentences can become compound by using words like "but, and, so, in addition, etc.", and all of these sentences are found to be using these kinds of verbs. A compound sentence is a sentence that should be using at least one verb to combine two or more sentences.