D．Be optimistic in the face of life's difficulties.

　　D　解析：写作意图题。通读全文可知， 文章讲述了作者因高血糖双目失明， 从此放弃了酷爱的绘画。但是， 他通过学习专为盲人和视力受损的人设计的电脑信息技术， 又重新燃起了希望。据此可以判断， 本文旨在告诉读者， 面对生活中的困难， 我们应当乐观积极， 故D项正确。A项意为"不劳无获"；B项意为"天生我材必有用"；C项意为"心之所愿， 无事不成"。

　　B

　　(2019·桂林、百色、崇左联考)By trying to tickle(使发痒) rats and recording how their nerve cells respond, Shimpei Ishiyama and his adviser are discovering a mystery that has puzzled thinkers since Aristotle expected that humans, given their thin skin and unique ability to laugh, were the only ticklish animals.

　　It turns out that Aristotle was wrong. In their study published on Thursday, Ishiyama and his adviser Michael Brecht found that rats squeaked and jumped with pleasure when tickled on their backs and bellies. These signs of joy changed according to their moods. And for the first time, they discovered a special group of nerve cells. These nerve cells made this feeling so powerful that it causes a rat being tickled to lose control.

　　To make sure that he had indeed found a place in the brain where tickling was processed, Ishiyama then stimulated(刺激) that area with electrical currents. The rats began to jump like rabbits and sing like birds.

　　"It's truly ground­breaking，" said Jeffrey Burgdorf, a neuroscientist at Northwestern University who reviewed the paper．"It takes the study of emotion to a new level．"

　　Burgdorf has played a central role in our understanding of animal tickling. He was part of a team that first noticed, in the late 1990s, that rats made special noises when they were experiencing social pleasure. Others had already noted that rats repeatedly made short and high sounds during meals. But the lab where Burgdorf worked noticed that they emitted similar sounds while playing. And so one day, the senior scientist in the lab said, "Let's go and tickle some rats．" They quickly found that those cries of pleasure doubled.

　　"The authors have been very adventurous，" said Daniel O'Connor, a neuroscientist at Johns Hopkins University. To him, that finding was very surprising.

　　"Why does the world literally feel different when you are stressed out？" he said．"This is the first step towards answering that question. It gives us a way to approach it with experimental rigor(严谨)．"

【解题导语】　本文是一篇说明文。文章中科学家通过刺激老鼠来记录它们的神经细胞的反应，所得出的结论将对情绪的研究提升到了一个新的高度。