Read the sentences. Grapefruits are citrus fruits. Lemons and oranges are also citrus fruits.
Which combines the sentences by using a compound subject?
Grapefruits, lemons, and oranges are citrus fruits.
Grapefruits and lemons are citrus fruits, and so are oranges.
Grapefruits are citrus fruits, and lemons and oranges are, too.
Grapefruits, in addition to lemons and oranges, are citrus fruits.

Grapefruits, in addition to lemons and oranges, are citrus fruits.

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.

the answer is bags.