You are correct! Acceleration involves a change in both direction and speed. When an object undergoes acceleration, it is experiencing a change in velocity, which is a combination of both speed and direction. So, option D, "both direction and speed," is the correct answer. To arrive at this answer, it helps to understand the definition of acceleration: it is the rate at which an object's velocity changes over time. By considering this definition, you can deduce that acceleration involves changes in both speed and direction.
