The condition of the Earth had to become favourable before it could support any form of life.
The formation of the different layers around the earth like the ozone layer was necessary before life could originate. Primitive species such as some prokaryotes were able to live in hydrothermal conditions during the initial times. With the passage of time, as the concentration of oxygen increased due to photosynthetic prokaryotes, situations became favourable for eukaryotic organisms to arise.
I believe that it's an exhausted bear. Cellular respiration is the way plants and animals receive energy. If the bear is exhausted, it means it's cellular respiration is lacking.
I think the answer is {b.false} Infectious diseases are diseases that spread from one person to other either directly or indirectly. I think this is the answer.
