<span>If two waves with identical crests and troughs meet, what is happening?
</span>C. Constructive interference is occurring.
An action-reaction pair would be a pair in which one of the elements exerts a force on the other element (action), and then the other element would respond to this force by exerting another force in the opposite direction (reaction).
From the given choices, we will see that:
For choice A, the moon exerts a force on the earth by pulling it (action) and the earth responds to this force by pulling the moon (reaction in opposite direction of the action).
Therefore, the correct choice would be:
A. <span>The Moon Pulls on Earth, and Earth pulls back on the moon.</span>
1) weight of the box: 980 N
The weight of the box is given by:

where m=100.0 kg is the mass of the box, and
is the acceleration due to gravity. Substituting in the formula, we find

2) Normal force: 630 N
The magnitude of the normal force is equal to the component of the weight which is perpendicular to the ramp, which is given by

where W is the weight of the box, calculated in the previous step, and
is the angle of the ramp. Substituting, we find

3) Acceleration: 
The acceleration of the box along the ramp is equal to the component of the acceleration of gravity parallel to the ramp, which is given by

Substituting, we find
