Bacteria are often helpful because they​

Yes it is helpful

Explanation:

Not only do we live in harmony with these beneficial bacteria, but they are actually essential to our survival. Good bacteria help our bodies digest food and absorb nutrients, and they produce several vitamins in the intestinal tract — including folic acid, niacin, and vitamins B6 and B12.

the correct answer is option d.

an appositive is a noun, noun phrase or noun clause which follows another noun or noun phrase in order to describe it or name it another way. they are usually used between commas, brackets or dashes.

the example sentence with the correct use of commas is the following:

her uncle, the man over there in the red shirt, owns the hardware store in town.