The Gulf Stream is a surface current that carries water to the northern Atlantic Ocean. It travels along the eastern United States before crossing the Atlantic Ocean. What are two factors that cause changes in the motion of surface currents like the Gulf Stream? (multiple choice answer)
a. The current reaches a barrier, such as a landmass.
b. The water gets colder, which decreases its density and causes it to rise.
c. Wind pushes on the water's surface.
d. The water gets saltier, which decreases its density and causes it to rise.

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