20.
consider the propulsion of a fish through the water. a fish uses its fins to push on the water. the reaction force is

a. the water pushing on the fish

b. the propulsion of the fish

c. the water propulsion

d. gravity on the fish

Consider the propulsion of a fish through the water. A fish uses its fins to push on the water. The reaction force is the water pushing on the fish

Option A

Explanation:

Action and reaction forces act on different bodies. Propulsion is nothing but the movement of a fish inside water. Fish gets the help of fins in moving water backward. As a result, the water thrown back exerts the same force on the fish. Hence, the fish moves in the forward direction.

This is clearly understood by Newton's 3rd law that states for any action, there exists an equal and opposite force, which is termed as reaction. Here, the push of the fish, on water, is the action, and the push of the water back is the reaction, which is the reason for its propulsion.

i think its c if i'm wrong

3. dark matter

empty space could also be a simple vacuum