If velocity is cut in half, how is the kinetic energy affected

Since the K.E proportional to the square of the velocity 
so if the velocity cut in half the K.E will equal 1/4 the initial value  

Using the Kinetic Energy formula:
K.E = 1/2 (mv^2)

It is shown that kinetic energy is directly proportional to the square of velocity. Which means that if the velocity was reduced to half, kinetic energy would be 1/4 of the original value. To state an example:

let: m = 1 ; v = 2

Substituting the values would give us:
K.E = 1/2 ((1)(2)^2)
K.E = 2

Halving the value of velocity would give us the following:
K.E = 1/2 ((1)(1)^2)
K.E = 0.5

As seen, K.E was reduced to 1/4 of the original value.

The answer is b hope this