There are some organelles which are found in plant cells but which are not found in the animal cells, these structures will provide a positive identification of a plant cell under a microscope.
The structures which would provide a positive identification of a plant cell under a microscope are CENTRAL VACUOLE, CHLOROPLAST [PLASTIDS] AND CELL WALL. These structures are only present in plant cells.
I think it's D. It shields life forms on the surface from radiation?
If you were studying climate change in general. The answer would be the last one which is ecosystem because it’s the study of the environment