The ozone layer to sustain terrestrial life by
a. absorbing incoming uv radiation
b. keeping levels of ozone in the troposphere low
c. maintaining the earth's temperature structure
d. all of the above

The answer is D. All of the above.

The ozone layer helps to sustain terrestrial life by; absorbing incoming UV radiation, keeping levels of Ozone in the troposphere low, and also maintaining the Earth's temperature structure. 

Ozone layer is a gas layer in the atmosphere that protects all living organisms on the Earth surface from harmful ultraviolet rays from the sun. Without it, it would be extremely difficult for organism to survive on the Earth's surface. It plays an important role in the temperature structure of the Earth's atmosphere. Without the filtering action of the ozone layer, more of the Sun's UV-B radiation would penetrate the atmosphere and reach the Earth's surface. 

The ozone layer helps to sustain terrestrial life by absorbing incoming UV radiation, keeping levels of ozone in the troposphere low, and maintaining the Earth's temperature structure.

Your answer is d. all of the above.