
Passage: British scientists wrote in the November 11, 2010 issue of the journal Nature and pointed out that they had found fossilized bacteria in Scottish rocks that might have lived about 1.2 billion years ago. This suggests that the concentration of oxygen on Earth has increased to the level needed for human evolution. This major event took place 1.2 billion years ago and it was 400 million years earlier than scientists previously thought. The new research is expected to give scientists a new understanding of the timetable for the evolution of the Earth's atmosphere and the life that depends on it for a living.
Question: Which of the followings is assumed by the above findings of scientists?
A. A.It was previously thought that human evolution took place about 800 million years ago.
B. B.The bacteria began to use oxygen in chemical reactions about 1.2 billion years ago to gain energy to survive.
C. C.The increase in the concentration of oxygen indicates that the organisms that dominate the earth have changed from simple organic matter to complex multicellular organic matter.
D. D.Only the concentration of oxygen in the atmosphere increases to a critical point can some bacteria survive.
Answer: