Carbohydrates, fats, proteins: these organic molecules all have this element in common. this element can form multiple bonds, and it bonds with other elements as well as with itself. this element is
a)
calcium.
b)
carbon.
c)
helium.
d)
hydrogen.

answer: c.

explanation:

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.