Final answer:
To keep balance with a book on your head, you should move your feet farther apart to increase stability by expanding your base of support and lowering your center of gravity.
Step-by-step explanation:
To maintain balance when carrying a load such as a book on your head, you would need to adjust your posture so that your center of gravity (cg) and the book remain above your base of support, which is your feet. Referring to figures and experiments mentioned, when people carry weight, they tend to lean in a certain direction to position their overall cg above their feet to maintain balance. For example, a father with his son on his back leans forward, a student with a shoulder bag leans to the side, and a student with an armful of books leans backward.
Based on these observations, to keep balance with a book on your head, you would likely move your feet farther apart to provide a larger base of support (option b). This adjustment lowers your center of gravity and increases stability, especially in the front-to-back direction where humans are less stable because our feet are not very long. By spreading your feet, you can more easily make minor adjustments to maintain balance without the danger of the book falling.