Answer:
D
Explanation:
Improve desirable traits and help determine the heritability of a trait.
Oxygen and carbon dioxide travels to and from tiny air sacs in the lungs, through the walls of the capillaries, into the blood. Blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs.

A mutation is one form of genetic variation.
Answer: Homologous chromosomes are the pairs of chromosomes that having same gene sequence, equal length of arms and centromere location. Homologous chromosomes have two homolog one come from male parent and other come from female parent.
Explanation:
These chromosomes Are formed for the purpose of genetic variations. They are called homologous because when two same structured exist it form pair together
Answer:
True
Explanation:
The stratosphere is the layer of the earth’s atmosphere which is above the troposphere and below the mesosphere.
The stratosphere contains about 90 percent of the ozone layer. The stratosphere is made up of ozone layers which helps in the absorption of about 95 percent of the ultraviolet rays from the sun and converting to heat.
This is the reason why depletion of the ozone layer found in the stratosphere gives rise to global warming.