D. Neither light nor moisture is good for food preservation, so most food products are packaged immediately after they are processed.
Explanation:
A comma shows a break or pause in a sentence. A comma is used to separate independent clauses therefore it can be said that the first and second half of the sentence in question can be said as two different sentences.
A comma brings together two phrases or clauses. It is a useful punctuation mark which is used to indicate to readers a certain separation of words, phrases, clauses or ideas in order to prevent misreading or misunderstanding what the writer intended to say. It is important to know where exactly in a sentence to insert a comma so you can convey the meaning of your sentence perfectly.
Gently because it describes the degree at which someone is tapping on the window sill, and that's what adverbs do, they describe a a verb by many different factors.
