Question

The hyphen in "one-time winner" is used because:
a. time modifies one winner
b. one is a prefix
c. one-time is a number
d. one and time modify winner

Answer 1

The hyphen in "one-time winner" is used because 

d.one and time modify winner

Hyphens are used in compound words to show that the component words have a combined meaning or that there is a relationship between the words that make up the compound.

Answer 2

The correct answer is D. one and time modify winner.

A is incorrect because time is the word being modified (described), and not the other way round. B is incorrect because one is a number, and not a prefix. C is incorrect because one-time is an adjective, and only one is a number.

That leaves us with D as the correct answer - both words, one and time, modify the word winner - and because it is a compound adjective, it has to have a hyphen.