Global average Ozone layer thickness isa.1 million DBb.100 DBc.Cannot be determinedd.300 DB

The question seems to be asking about the average thickness of the Earth's ozone layer. However, the units provided (DB) do not make sense in this context. The thickness of the ozone layer is usually measured in Dobson Units (DU), not DB.

The average thickness of the ozone layer is approximately 300 DU, which is equivalent to a layer of pure ozone 3 millimeters thick at standard temperature and pressure. So, the closest answer to your question would be 300 DU, not DB. However, this option is not provided in your list.

Therefore, the correct answer to your question with the provided options is: c. Cannot be determined.