The answer that you are looking for is A. Nephrons
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.
The official answer is both Heart Disease and Cancer.
