For a plane to be able to fly clockwise in a horizontal circle as seen from above, in addition to exerting a force downwards on the air
1) it must be increasing its speed.
2) it must exert a force on the air that is directed to the plane's left side.
3) it must exert a force on the air that is directed to the plane's right side.
4) it does not need to exert a force: it must only move the wing flaps out.
5) it only needs to deflect the air without exerting any additional force on the air.
Answer: 2