Which part of speech is the underlined word?

That's what a fast is—a period of time during which you do not eat.

A.
conjunction

B.
adverb

C.
preposition

D.
noun

fast is the underlined word

Question

Which part of speech is the underlined word? 

That's what a fast is—a period of time during which you do not eat.
 
 A.
conjunction
 
 B.
adverb
 
 C.
preposition
 
 D.
noun

fast is the underlined word

pinkcandyrosez882 · Answer

Would you say that the word "fast" is a noun (thing), a preposition (place or time relating to noun), an adverb (word describing an action), or a conjuction (word that joins two sentences; like 'and' or 'but')?

anonymous · Answer

ok

pinkcandyrosez882 · Answer

Sorry I don't want to just say the answer without explaining