Compared with surface currents, deep currents are a. colder and less dense. c. warmer and denser. b. warmer and less dense. d. colder and denser. select the best answer from the choices provided a b c d

The correct answer is option d, that is, colder and denser.  

The surface currents refer to the currents at the surface of the water, to a few hundred meters deep, while deep currents refer to the currents when the density increases to a greater extent.  

The surface current takes place close to the surface and move horizontally. This kind of currents are caused by global winds, an example of surface current is Gulf Stream. On the other hand, deep current takes place in the ocean and is affected by the density of water, temperature, and salinity. An example is Antarctica Bottom Water. In comparison to surface currents, deep currents are colder and denser.  

i think it's letter a.