I need some help with Direct linear variation.

I had tooken a test, and one of the questions on there said
" Which equation represents a direct linear variation?" The answers were
A ; y = 1/x
B ; y = x + 2
C ; y = x squared
D ; y = 1/2x .
I choose B . But now it says i got that wrong and the correct answer is D . How is that ?

Are u sure its direct variation or is that an incomplete question?