A study of traffic safety shows a correlation of 0.57 between average speed of traffic and number of fatal accidents for a particular stretch of highway. This means that
a. drivers should speed up to get through this area as quickly as possible.
b. as speed increases, fatalities decrease.
c. fatalities tend to increase as average speed increases.
d. every 1 mile per hour increase in average speed increases the number of traffic fatalities by .57.