I think it is D. I hope this helps
<span>The correct answer is B - Light can travel in a vacuum, and its speed is constant if the source is moving or stationary.</span>
Answer: Gamma rays
Explanation: The given waves belong to the electromagnetic spectrum which consists of different electromagnetic radiations arranged in terms of increasing wavelengths or decreasing frequencies.
Thus 
E= energy
= frequency
c = speed of light
= wavelength
Thus frequency and wavelength are inversely related. The waves having high energies ave high frequencies and have shorter wavelengths.
Thus gamma rays having highest energy have highest frequency and shortest wavelength.
The amount of energy before and after any energy transformations remain the same because energy cannot be created or destroyed. From the law conservation of energy; any time energy is transferred between two objects, or converted from one form into another, no energy is created and none is destroyed. The total amount of energy involved in the process remains the same.
The frictional force is always act in opposite direction of motion. if wheels is moving in +x axis or right then the f force is act in -x or left
