Why do humid tropical regions have only small variations in temperature throughout the year?

Why do humid tropical regions have only small variations in temperature throughout the year?
 
  A) The canopy of trees in the rain forest shade the ground and reflect light all the time.
  B) The cloud cover and rain do not allow the temperatures to rise or fall significantly.
  C) The winds associated with these systems rapidly redistribute the heat.
  D) The location of this climatic region is limited to an area where the solar radiation does not vary significantly.
  E) The constant humidity maintains a relatively uniform temperature.