If you put each of the possible answers in the blank and read the sentence the right answer would be C.
In the context of an adjective used to describe pain, we can look at the answer choices:
Silent pain seems like an odd choice for someone to notify a doctor about, so that is probably not the answer.
Thoughtful does not describe pain.
Responsive does not describe pain.
Severe pain would be a reason for someone to notify a doctor, so this is likely the correct answer choice.
Answer:
D. Sustenance
Explanation:
Livelihood is the course of ones life. Sustenance is the support you gain by food and drinks.
The paragraph suggests that the shepherd wants to put down the dog and end its course of life.
A. Shelter ❌
B. Enjoyment ❌
C. A treat ❌