I would say C. The passage is talking about death and C is the only one that mentions death.
This words simply means not easily convinced. Or even having doubts.
The beginning starts off with "has taught" indicating a foreword. The passage also talks about past achievements and accomplishments.
Which two sentences in this excerpt from Leo Tolstoy's The Death of Ivan Ilyich show Ivan Ilyich's struggle with his life and his inability to let go of his past?
For three whole days, during which time did not exist for him, he struggled in that black sack into which he was being thrust by an invisible, resistless force. He struggled as a man condemned to death struggles in the hands of the executioner, knowing that he cannot save himself. And every moment he felt that despite all his efforts he was drawing nearer and nearer to what terrified him. He felt that his agony was due to his being thrust into that black hole and still more to his not being able to get right into it. He was hindered from getting into it by his conviction that his life had been a good one. That very justification of his life held him fast and prevented his moving forward, and it caused him most torment of all.
Suddenly some force struck him in the chest and side, making it still harder to breathe, and he fell through the hole and there at the bottom was a light. What had happened to him was like the sensation one sometimes experiences in a railway carriage when one thinks one is going backwards while one is really going forwards and suddenly becomes aware of the real direction.
"Yes, it was not the right thing," he said to himself, "but that's no matter. It can be done. But what is the right thing? he asked himself, and suddenly grew quiet.
