The best statement would be number 3. Sound waves move perpendicular to the medium particles.
Answer:
a) 
Explanation:
t = Time taken
u = Initial velocity
v = Final velocity
a = Acceleration

The acceleration of the bicycle and rider is -1.5 m/s²
Force

The magnitude of the average force needed to bring the bicycle and its rider to a stop is 
(a) 1200 rad/s
The angular acceleration of the rotor is given by:

where we have
is the angular acceleration (negative since the rotor is slowing down)
is the final angular speed
is the initial angular speed
t = 10.0 s is the time interval
Solving for
, we find the final angular speed after 10.0 s:

(b) 25 s
We can calculate the time needed for the rotor to come to rest, by using again the same formula:

If we re-arrange it for t, we get:

where here we have
is the initial angular speed
is the final angular speed
is the angular acceleration
Solving the equation,

The answer is D. Isotopes.
Hope that helped.