Which of the following examples have a constant rate of change?

A : You drive from Colorado to Texas. In the first 4 hours, you cover 240 miles, and in the second 5 hours, you cover another 240 miles.

B : The money you put in the bank earns 5% Interest. This means that the bank pays you 5% of the amount of the money kept in the bank each year.

C : A salesperson earns $50 plus $10 for every $100 of merchandise he sells.

D : The amount bacteria double every hour.