Which best describes the purpose of a controlled experiment? A) to make sure the results of the experiment support the hypothesis
B) to prevent a dangerous condition resulting from a reaction
C) to examine whether one variable causes a change in another
B) to prevent an undesired change in a variable

d.)

Explanation:

if it were to be uncontrolled many other variables could enter the experiment

note: the given question is incomplete.

complete question is given below.

which is an example of kinetic energy?

a. the energy stored in ethanol  

b. a hockey puck sliding across the ice  

c. a compressed spring  

d. a ball sitting at the top of a ramp

solution: the kinetic energy is the energy posses by the virtue of the motion of the object.

in the given options, a, c and d are the example of potential energy because it is the energy posses by the virtue of the rest of the object. but option b has the kinetic energy as the object is in motion.

hence, a hockey puck sliding across the ice   is the apex example of kinetic energy.

so, the option (b) a hockey puck sliding across the ice   is the correct option.