1. At first, Oxygen wasn't present on Earth. But in time, plants started to grow at the bottom of the seas and produce Oxygen during photosynthesis. As there was Oxygen, the first animals appeared. After a while species evolved and come out of the sea, being able to breathe outside of it because they developed lungs.
5. Mean-a)average. Bed-b)bottom of the sea. Mass-c)amount of matter in a body. atmosphere-a)a mixture of gases.
6.noun+noun-bedroom. Noun+gerund-drawing. Adj+noun-software. Gerund+noun- helping hand. Noun+preposition-addiction to. Vb+noun-washing machine
