The right answer is:

a) proof of work
b)by transactions fee (coins are not created since they are pre-mined)
c) a correct answer could be: proof of capacity, proof of elpsed time, proof of burn
The reward of this post was 0.21 SBD.

There are no BEST answer. The answer of the user @killer369 is not totally correct (the second one is wrong since in proof of stake validators are paid in transaction fees) but the answer of @killer369 is quite complete and add value. So it will be counted as BEST ANSWER.
The reward of the BEST answer is 25% of 0.21 = 0.0315
The reward of the first answer is 10% of 0.21 = 0.021
The reward of the upvotes on best answer is 25% of 0.21 = 0.0525 which id divided to users: @jessy93 @shyal
Thank you all for participating and for your contributions.