Even Though the Autumn May Be Unusually Warm, the Leaves

Multiple Choice

Even though the autumn may be unusually warm, the leaves from deciduous trees begin to drop during September.Which of the following is the best explanation?

A) The trees are responding to shorter days.
B) The autumn months are usually drier because the summer rains have tapered off.
C) The effects of phototropism are operating "right on schedule."
D) There is not enough sunlight to carry on photosynthesis any longer.
E) None of these are the best explanation.