Answer:
Option C.
Explanation:
A proportional relationship is defined as


where, k is the constant of proportionality.
From the given graph it is clear that there is proportional relationship with the point (-20,40).
Substitute x=-20 and y=40 in the above equation to find the value of k.

Divide by -20.

The value of k is -2. So, the proportional relationship is defined as

At x=-40,

It means point (-40,20) would not form a proportional relationship with the (-20,40).
Similarly,
At x=-10,

At x=15,

At x=5,

It means points (-10,-20) and (5,-15) would not form a proportional relationship with the (-20,40).
Only point (15,-30) would form a proportional relationship with the (-20,40).
Therefore, the correct option is C.