Answer:
The best answer is A. The midbrain detects and processes information from the environment and sends signals to leg muscles to change their rate of contraction.
Step-by-step explanation:
This is because the midbrain is responsible for processing sensory information from the environment and coordinating motor responses, such as adjusting the rate of contraction of leg muscles to run faster. In this case, the boy's midbrain would have detected the change in weather and the sensation of raindrops on his skin, and sent signals to his leg muscles to increase their rate of contraction in order to run faster and avoid getting drenched.
Option B is incorrect because sensory information does not bypass the brain and go directly to the spinal cord. Option C is incorrect because the hypothalamus is primarily responsible for regulating bodily functions such as hunger, thirst, and temperature, and would not be directly involved in the boy's response to rain. Option D is also incorrect because the visual cortex is responsible for processing visual information, not sensory information from the skin.