The correct answer is d. 3.5 billion years.
Prokaryotes were the first forms of life on Earth long before simple multicellular life appeared because of their ability to withstand extreme conditions. It is believed that the first living forms were bacteria combined with archaea in the microbial mat (multi-layered sheet).
Natural selection means that the organisms better adapted to their environment, that is, they have developed the right characteristics/skills/response to the external ambient, have higher chance to survive, making the next generations genetically inherit such acquired surviving characteristics.
These generations will thus have a higher chance of survival, making these species being "naturally selected" as survivors, while those who haven't or are slower in this process, have a higher risk of elimination.
As the flower takes water that it needs to survive, the dye in it has no more density so it goes up with the water dying everything in its path blue.
