Answer:
A
The day is their night and the night is their day, when I shout and they shout back I run away.
I am a king but also a common device of measure. What am I?
Passed from father to son and shared between brothers, its importance is unquestioned though it is used more by others.
A precious gift, yet it has no end, no beginning, and nothing in the middle.
All about, but cannot be seen, Can be captured, cannot be held, No throat, but can be heard. Who am I?