Scientists think that algae first evolved approximately 2.7 billion years ago, and soon after this oxygen began to exist in the atmosphere. Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere.
Explanation:
It is a. Esta because you are saying it is there.
Answer:
A) Do unto others what you would have them do to you.
Explanation:
D. mejor, because it's irregular
