A car is traveling on Interstate 80, and suppose we choose the positive x-direction to be east. In which of the following situations is the average acceleration of the car negative?

A. The car is initially going 10 m/s east and then, at a later time, goes 30 m/s east.
B. The car is initially going 30 m/s east and then, at a later time, goes 10 m/s east.
C. The car is initially going 30 m/s west and then, at a later time, goes 10 m/s west.
D. The car is initially going 10 m/s east and then, at a later time, goes 30 m/s west.
E. Two of the above.