Vitamin A is a group of unsaturated nutritional organic compounds, that includes retinol, retinal, retinoic acid, and several provitamin A carotenoids, and beta-carotene. Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision.itamin A can be found in two principal forms in foods 1  : Retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance. 2  Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinyl ester.
pure tone is a tone with a sinusoidal waveform reciting tone such as psalm tone and recitative as in gregorian chants timbre the quality of a musical note or sound that distinguishes different types of sound production tonality a system of music based on a key center or tonic tone control a typically electronic control for affecting frequency content of an audio signal tone linguistics the pitch and pitch changes in words of certain languages tone musical instrument the audible characteristics of a musician s sound
A ringtone or ring tone is the sound made by a telephone to indicate an incoming call or text message. Not literally a tone nor an actual ring any more, the term is most often used today to refer to customizable sounds used on mobile phones.