Answer:
The correct answer is option D) "response to external stimuli".
Step-by-step explanation:
The phenomenon of tree shedding their leaves during the autumn months is an example of plants response to external stimuli. The deciduous trees start shedding their leaves when light levels and temperatures drop, as a result of the flow of auxin being reduced and the levels of the hormone ethylene rise in the leaves. This process allows the trees to survive winter by conserving resources and protecting from being blown by the winds.