Questions: Thin lines that show solid, cutaway surfaces in a section view are called lines.

The answer is the third one: object lines.

Explanation for each option:

1. Section lines: These are not the correct answer. Section lines are used to indicate the areas of a part that have been cut through in a section view, but they are not the thin lines that show solid, cutaway surfaces.

2. Cutting plane lines: These lines indicate where the section is taken, but they are typically thick lines and not used to show the solid, cutaway surfaces themselves.

3. Object lines: These are the correct answer. Object lines are used to represent the visible edges of an object. In a section view, thin lines that show the solid, cutaway surfaces are typically object lines.

4. Hidden edge lines: These lines are used to represent edges that are not directly visible, but they are not used to show solid, cutaway surfaces in a section view.

In summary, the thin lines that show solid, cutaway surfaces in a section view are called object lines.