What Function Does the Upper Atmosphere Ozone Layer Serve

What function does the upper atmosphere ozone layer serve?

A) It protects against the sun's harmful ultraviolet radiation.
B) Its gases trap heat in the earth's atmosphere leading to the greenhouse effect.
C) This atmospheric layer provides a rich source of CFC used as a refrigerant to fuel air conditioning units.
D) The ozone layer is the source of oxygen needed to breathe.