20. ten horses sleep in the same
barn. after one week, one of the horses
becomes sick, but the others do not.
what kind of disease does the sick horse
probably have?

The horse has  a non-communicable disease.

Explanation:

In the given situation, only one horse is effected this suggest that the cause of the disease is not present in any other horse.Though the horses were sleeping in same barn and sharing the same resources they did not get the disease. This clearly states that the disease does not spread from one individual to other but remains confined to only effected individual.Thus it is a non infectious or non-communicable disease.