The most controversial issue? How can plants respond in this way? Humans and other advanced animals integrate signals from their environment through the nervous system and brain, and respond. But plants have no nervous system and no brain, so they must be done by other means. The most likely explanation is, Their response relies on the reception of certain hormones and electronic signals, and a coordinated feedback system. It can be inferred from the above. Next, the question that the author is most likely to express? ['A detailed description of how animals respond to external stimuli.', 'Animals and plants have different sensitivities to external stimuli.', 'Relevant research on plants responding to external stimuli by coordinating with certain hormones and electronic signals.', 'Relevant scientists have huge differences in how plants respond to external stimuli.']