Answer: C. Cyrosphere and biosphere
Step-by-step explanation:
Caribou are members of the Earth's Biosphere which is an umbrella term for all living organisms on Earth.
The Cyrosphere refers to any and all areas of Earth where water is in frozen form.
David learning that Caribou need deep frozen ice to walk on is therefore an interaction of these two systems as it shows a living organism being the Caribou interacting with deep frozen ice which is part of the Cyrosphere.