Surface currents are caused by
a. floods.
c. the wind.
b. warm water.
d. the equator.

Surface currents are caused by the wind - answer c.
The wind in turn can be caused by other factors, such as the spin of the earth. The wind affects only the top 100 meters of water, deeper currents are caused by density differences of water.

C. Wind

Surface ocean currents are caused by the different patterns of the wind. Because of the earth’s rotation, wind doesn’t simply circulate in a back and forth motion but it moves in varying directions in the Northern and Southern hemispheres. These deflected wind movements result in a curved pathway. This is called the Coriolis Effect.

Surface ocean current form gyres or large circular patterns. Because of the Coriolis Effect, gyres flow differently depending on which hemisphere they are on. Those who are on the Northern hemisphere move clockwise, while those in the Southern hemisphere circulate counter clockwise.