It exists above mesosphere and below exosphere, absorbs much of the solar radiation, auroras occur here and is often considered as the outer space. This is
A) troposphere
B stratosphere
C) mesosphere
D) thermosphere

well the answer is 2!

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.