Jenny is trying to describe a wave. Which example would be the best description? a toy car hitting a wall and bouncing back
a toy car rear-ending a toy car that then rear-ends another toy car
two toy cars driving parallel to each other at the same speed
two toy cars driving away from each other at the same speed

A toy car rear-ending a toy car that then rear-ends another toy car.

Explanation:

Waves move forward and make the water go up and down.

Hope this helps, it's a little weird to explain :S

a toy car rear-ending a toy car that then rear-ends another toy car

Explanation:

all waves carry energy, and the cars bumping into each other transfers energy from one car the the next. it is like a transverse wave, the wave will go perpendicular like a spring moving up and down, dominos tipping over, or a car hitting another car.