The best title for the text may be______.
A) Use Humor Effectively C) Add Humor to Speech
B) Different Humor Strategies D) Various Kinds of Humor

A．illustrate the effects of movements in the upper layer of the earth
B．show how temperature differences depend on the positions of the continents
C．describe the complicated motions made possible by the ocean currents
D．account for the rising currents under min-ocean ridges

A．Spreading of ocean trenches.
B．Movements of min-ocean ridges.
C．Sinking of ocean basins.
D．Differences in temperature under oceans and continents.