The correct answer is C. Pestilent
Step-by-step explanation:
In the excerpt presented, the word "morbid" is used to describe cholera, which is a disease that can lead to death. About this, the author explains this can be passed from one person to another by direct contact or even at distance.
Also, the author uses the terms "morbid matter" and "morbid poison". The use of "morbid" refers to how lethal, unhealthy, or negative the disease is. This word can be related to the word "pestilent" which means "deadly". According to this, the meaning of morbid is pestilent.