The correct answer is A. Decibels.
Decibels (dB) are a logarithmic unit that is used to express the ratio of two values of a physical quantity, often power or intensity. In the case of sound, decibels are used to measure the intensity of a sound wave, which is a measure of the amount of energy that is carried by the wave. The higher the decibel level, the more intense the sound.
Lux is a unit of illuminance, which is a measure of the amount of light that is incident on a surface. Illuminance is equal to the luminous flux per unit area, and is measured in lumens per square meter (lm/m2).
Parsec is a unit of astronomical distance, and is equal to the distance at which one astronomical unit (AU) subtends an angle of one arcsecond. One AU is the average distance between the Earth and the Sun, and is equal to 149.6 million kilometers.
Candela is a unit of luminous intensity, which is a measure of the amount of light that is emitted by a source in a particular direction. Luminous intensity is measured in candelas (cd), and is equal to the luminous flux per unit solid angle.