Answer: The answer is C. For each year since 1970, passenger car fuel efficiency has increased by 0.29 miles per gallon.
Explanation:
In a linear model of the form y = mx + b, m is the slope and b represents the y-intercept.
In this situation, 0.29 is the slope.
The slope is the ratio of the change in y to the change in x.
In context, the slope indicates an increase of 0.29 miles per gallon per year after 1970.
Therefore, the slope means that for each year since 1970, passenger car fuel efficiency has increased by 0.29 miles per gallon.