Which scientific term best matches this description: Unit of length in the International System of Units (SI), equal to one billionth (10^{−9}) of a meter?

A) radian (rad)

B) scientific notation

C) second (s)

D) nanometer (nm)

Answer: D

Explanation: A unit of length in the International System of Units (SI), equal to one billionth (10^{−9}) of a meter. It is often used to express dimensions on an atomic scale, such as the diameter of a helium atom (0.06 nm), and to specify the wavelength of visible light, which ranges from 400 to 700 nm.