Answer: B. Slower population growth
Explanation:
Slower population growth is Not a reason why communicable diseases like pneumonia kill fewer people today than they did in the past, this is because in present times irrespective of the population growth, newer approaches have been introduced to improve quality of life and hence reduce the risk of communicable diseases.
Approaches like; continuing medical advances, improved living conditions, better preventive treatment. Etc.
Highest risk body fluid would be blood because it has high nutritional value and pathogen is multiplying on there. Most pathogen will be transmitted by blood.
Droplet from cough also highly contagious since it easily contacts with any part of the body. Inhalation also makes the infection easier since it contacts mucosa.
Vaginal secretion and seminal fluid can transmit many virus but it depends on how many virus in the blood.
Saliva is composed by water and enzyme so it's low risk on virus spread. But it's on the mouth(which wasn't sterile) so it can be contaminated by various things.
In normal condition urine and spinal fluid is sterile, but in a case of infection, it can be contaminated.
Sweat is mostly water and salt so it's safe.
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