Answer:
 a. The graph has a constant of variation of 3, so it represents a direct variation.
Explanation:
We have been given a graph and we are asked to find whether our given graph represents direct variation or not. 
Since we know that a direct variation is an equation in slope-intercept form, which passes through origin (0,0) and constant of variation equals to the slope of the line. 
Direct variation equation is in form: 
, where k= constant of variation.
Slope intercept equation of line is in form: 
, where m= slope and b= y-intercept. 
Let us find equation of our given line in slope-intercept form.
We can see from our given graph that our line passes through the origin, so y-intercept (b) equals zero. 
Let us find slope of our given line. 

 

Upon substituting m=3 and b=0 in slope intercept form of equation we will get: 
. Upon comparing our line with direct variation equation we can see that k=3, therefore, option a is the correct choice.