Answer: E. Linear.
Explanation:
Linear functions are straight, and in this case, Ian deposits $10 dollars every month. That means that if this is a linear function, it would be modeled by the equation y = 10x.
This cannot be an exponential function because the money is not growing exponentially, curved way too fast.
This cannot be a quadratic function, which looks like a U-shape.
This cannot also be a square root, which is a curve function and has no sense with this type of problem.