system engineering Which of the following correctly describes a function?

A$.$ Specific action necessary to achieve a desired objective or input$-$output transformation; always expressed as a verb phrase.

B$.$ The structure of components, their relationships, and the principles and guidelines governing their design and evolution over time.

C$.$ Assignment of functional and non$-$functional requirements from the system level to down to the appropriate lower$-$level system elements.

D$.$ Pictorial representation of the structure of a system$$s functional and non$-$functional requirements along with the evaluation measures used to quantify a system$$s performance in meeting those requirements.