Fill in the Blank with One of the Words or Phrases

Multiple Choice

Fill in the blank with one of the words or phrases listed below.
-In the equation $\mathrm { y } = \frac { \mathrm { k } } { \mathrm { x } }$ , $\mathrm { y }$ variesـــــــــــــــ as $x$ .

A) directly
B) opposites
C) inversely
D) jointly