Which of the following statements do scientist believe to be true? ?

It has to be B, though i'm not sure of that fact, just by the process of elimination. life began around 3 billion years ago i think; the largest extinction was not at the end of the 20th century (8 years ago....) but in the cambrian period or somesuch; and microorganisms are definitely not generated by a life force in the air, but by themselves reproducing.