To solve this question, the user needs to understand analogies. An analogy is a comparison between two things that are similar in some way. In this case, we are comparing a car to its parts, and we must find the part of the human body that is similar to the car's chassis.

The chassis is the main framework of a car, which supports the body and other components. Therefore, the correct answer is the part of the human body that serves as the framework or support system for the rest of the body.

Now, let's go through each option and explain why it is right or wrong:

A. Skin: This option is incorrect because skin is not a support system for the body. While it does cover and protect the body, it is not a framework that supports other components.

B. Blood: This option is incorrect because blood is not a support system for the body. While it does transport nutrients and oxygen throughout the body, it is not a framework that supports other components.

C. Brain: This option is incorrect because the brain is not a support system for the body. While it is the control center for the body, it is not a framework that supports other components.

D. Skeleton: This option is correct. The skeleton is the framework of the human body, providing support and structure for the rest of the body. Therefore, the correct answer is D.

The Answer is: D