Looking at the problem, we see that our constant rate is 999/1000 because the pressure is only nine hundred ninety-nine <em>hundredths</em> of the previous pressure. Since this is a rate, it can't be a linear function, so eliminate C.
Now, look at the rate. 999/1000 < 1, which means that the function is decreasing as the x values approach infinity or grow larger. That is an indication that this is an exponential <em>decay</em>.
