Is not relevant, let alone correct. Helen Keller had much to say about being both blind and deaf, yet that was not the main part of why she was famous. She was admired for the rich inner life she developed for herself. B is not the answer.
A
John Milton was a very religious man. He cared little about what the results of his writing was. He cared mostly about uncovering the truth of his findings. He had a mostly humble nature about him. A is not correct.
D
He doesn't mention personal gain anywhere. This is more a lament at the loss of his sight when he is at the height of his power.
C
He worries that he will no longer be productive. C is your answer.
