To find the rate at which the dealership sold cars per month, we can divide the total number of cars sold by the number of months:
\[ \text{Rate} = \frac{\text{Total cars sold}}{\text{Number of months}} = \frac{159 \text{ cars}}{3 \text{ months}} = 53 \text{ cars per month} \]
Therefore, the answer is:
C. 53 cars per month