Thermoclines in oceans are best developed at a. lower longitudes. b. higher longitudes. c. lower latitudes. d. higher latitudes.

The correct answer is option C, that is, lower latitudes.

Explanation:

A thermal layer also called thermocline refers to a thin but different layer in a huge water body like in an ocean or lake, in which there occurs a brisk change in temperature with depth in comparison to the layers below or above it. In the oceans, the thermoclines are best developed at lower latitudes.  

The elements, which influence the thickness and depth of a thermocline comprise latitude, seasonal weather variations, and local environmental conditions like currents and tides.