Final answer:
The layer in question from question 17 is part of Earth's internal structure, which includes the crust, mantle, outer core, and inner core. The specific layer would be identified based on its relative position as mentioned in figure 12.1.1.
Step-by-step explanation:
In question 17, the layer in question is located within Earth's interior, which includes several distinct layers: the crust, the mantle, the outer core, and the inner core. Given the options provided: (a) crust, (b) mantle, (c) outer core, and (d) inner core, we would need to refer to the specific question details to accurately determine the correct answer. However, the information provided indicates that we are discussing a substantive layer of Earth, which would likely be the mantle or one of the cores, rather than the thinner crust. If figure 12.1.1 is correctly aligned with question 17, then we can infer the layer it refers to by its position relative to other layers.