Final answer:
The true length of a line that is parallel to both the horizontal and vertical planes can be observed in the top view of an engineering drawing.
The correct answer is a. front view.
Step-by-step explanation:
When a line is parallel to both the horizontal plane (hp) and the vertical plane (vp), its true length can be seen in the top view. This is because in the coordinate system of engineering drawing, a line parallel to both planes will appear in its true length when viewed from the top as it extends horizontally and is not foreshortened by perspective or angular views.
In other forms of engineering drawings, when considering other orientations, for example, a line parallel to the vp but inclined to hp would show its true length in the front view, and a line that is perpendicular to both vp and hp would show its true length in the side view.
When a line is parallel to both the horizontal plane (hp) and the vertical plane (vp), we can find its true length in the front view. In the front view, the line is projected onto the horizontal plane, giving us an accurate representation of its length.
For example, if we have a line that is parallel to the ground (horizontal plane) and a wall (vertical plane), we can measure its length in the front view.