Which are the "v" and "w" prepositions
a. via, with, within, without
b. vice, walk, went, where
c. wither, what, vast
d. whale, wonder, vanish via

In B, "walk" is not a preposition, It's a verb >>we reject the answer.
In C, "wither" is not a preposition. >>we reject the answer.
In D, "whale" is not a preposition, it's a noun. >>we reject the answer.

so A is the correct asnwer!

ps. it there are also other problems in the rejected answers, for example, "wonder" is a verb, but one false word is enough, so I just gave an example.