Decibels measure sound(a) intensity(b) frequency(c) loudness level(d) all of the above (8.5)

Decibels measure (c) loudness level.

Here's why:

Decibels (dB) is a logarithmic unit that is used to describe a ratio. In terms of sound, it is used to measure the loudness (or amplitude) of the sound.

(a) Intensity: While it's true that decibels can be used to describe the intensity of a sound, intensity is a specific term that refers to the power of the sound wave per unit area. It's not the same as loudness, which is a subjective perception.

(b) Frequency: Decibels do not measure frequency. Frequency, measured in Hertz (Hz), refers to the pitch of the sound, or how many times a sound wave cycles per second.

So, the answer is (c) loudness level.