Answer:
The answer is A
Step-by-step explanation:
A proportional function is a function where the output = constant x input
Let's make each of these situations into an equation
A) y = 3.5x
B) y = 40x + 25
C) y = 2x + 56
D) y = 2x + 5
because A is the only one that follows the output = constant x input rule it is the example of a proportional function