Variation means difference in genetic makeup between individuals within a specie.
There was no life on Earth for the first billion years because the atmosphere was not suitable for life. Earth's first atmosphere had lots of water vapor but had almost no oxygen. Later, frequent volcanic eruptions put several different gases into the air.
Nucleic acids store and transmit genetic information that you inherited from your parents.
Answer: [A]: "axon" .
______________________________________________________________
"The <u> axon </u><u /> is a thin fiber that carries signals away from the cell body."
______________________________________________________________
