The answer that you are looking for is C.
Exponential.
One way to think about this, is to ask how much you will lose each year. The first year you're losing 20% of $20,000 ($4,000). The second year you're losing 20% of 16,000 ($3,200). The dollar value your car loses each year diminishes exponentially, so it is not a linear but an exponential function.
C socks, and boots.
Because it could be cold outside?
