The rate at which velocity changes is called
a. speed.
b. vectors.
c. acceleration.
d. motion.

The answer is acceleration.

Acceleration is the rate at which velocity changes over time. The relationship between acceleration and velocity is presented in the formula:
a = Δv/Δt
The SI unit of acceleration is m/s² derived as following:
a = Δv/Δt [ = ] (m/s)/s = m/s * s = m/s²

Answer sample (c); // would be best because the percentage of the energy in an incident wave that remains in a reflected wave from this material is the smallest;

B) erini just took the test and it is correct