Which statement best defines an angle in standard position?

• A. An angle whose sides are both on the $x$-axis.
• B. An angle measured only in degrees between $0$ and $90$.
• C. An angle that always has its vertex at the origin and its terminal side along the negative $y$-axis.
• D. An angle formed by rotating a ray about its endpoint from the positive $x$-axis to a terminal side.

Answer: (D)

Verified step by step guidance

1. Understand that an angle in standard position is defined by its vertex and the position of its initial and terminal sides.
2. Recall that the vertex of an angle in standard position is always placed at the origin of the coordinate plane.
3. Recognize that the initial side of the angle lies along the positive x-axis.
4. The angle is formed by rotating the initial side about the origin to a terminal side, which can be anywhere in the coordinate plane depending on the angle's measure.
5. Therefore, the best definition is: an angle formed by rotating a ray about its endpoint from the positive x-axis to a terminal side.