The correct options are
A flow of energy through trophic levels
B recycling of nutrients
C waste decomposition
Ecosystems support the entire life on earth in many ways. They help in the energy flow through various stages and also help to recycle nutrients. Ecosystems help to maintain the natural balance of waste generation and waste decomposition and also help in climate regulation.
Shielding the earth from harmful UV components of sunlight is a function of the ozone layer.