This particular question or problem can be likened to a deductive reasoning. The viral disease known as HIV stand for Human Immunodeficiency Virus which is a disease that damages the immune system of anyone affected with the disease. The Human Immunodeficiency Virus goes through four main stages or steps that is to say the infection stage/step, the stages in which the symptoms does not show, the stages at which the symptoms start to show and the stage at which the Human Immunodeficiency Virus goes or turns to AIDS.
The frequencies of these "resistance genes" In human populations where HIV infection is common will increase. When Human Immunodeficiency Virus infection is common, people in that particular society will develop more resistance to the virus and the survival of the fittest is taken into account as people with more resistance tends to be more healthier than the ones with less resistance.
squamous epithelium consists of a single layer of flat cells. It is found in lungs,heart and blood vessels.It allows the movement of materials across it.
stratified epithelium has many layer of flat cells.It is present in lining of oesophagus and mouth and also over the skin
