Three objects are brought close to each other, two at a time. When objects A and B are brought together, they attract. When objects B and C
are brought together, they repel. From this, we conclude that (a) objects A and C
possess charges of the same sign. (b) objects A and C possess charges of opposite sign.
(c) all three of the objects possess charges of the same sign. (d) one of the objects is
neutral. (e) we need to perform additional experiments to determine information
about the charges on the objects.

the part of the wave he is travelling on is the crest

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.