Question

newtons first law of motion
newtons second law of motion
newtons third law of motion
the harder the stationary balls are struck by the moving ball, the more the ball at the opposite end will accelerate.
the moving ball exerts a force onto the stationary balls that is equal in magnitude and opposite in direction to the force the stationary balls exert on the moving ball.
the ball at the other end of the cradle will remain at rest until the line of balls is struck by the ball at the opposite end.

Explanation:

The first statement relates to Newton's second law ($F = ma$, more force leads to more acceleration). The second statement is Newton's third - law (action - reaction forces). The third statement is Newton's first law (an object at rest stays at rest until acted upon by a force).

Answer:

The harder the stationary balls are struck by the moving ball, the more the ball at the opposite end will accelerate. - Newton's second law of motion
The moving ball exerts a force onto the stationary balls that is equal in magnitude and opposite in direction to the force the stationary balls exert on the moving ball. - Newton's third law of motion
The ball at the other end of the cradle will remain at rest until the line of balls is struck by the ball at the opposite end. - Newton's first law of motion