C

    I'm a 34-year-old man. I lived in a nice house and have a successful career. But my life was not always so great. I had trouble learning from an early age. The school life was difficult for me.

    My life improved quickly when I discovered art. The art world gave me a chance to express myself without words. I went to an art school and became good at making things with dough. Here I learned my first important lesson: although I had trouble learning, I could still be smart and well express myself with dough. And I became confident from then on.

    I got my next lesson from rock climbing. It was a fun thing but I was frightened from the start. After about five years of climbing, I learned that if you fall in love with something and do it all the time, you will get better at it.

    Later I decided to learn how to read. Every day I practiced reading. After two hard years, I did well in it. And reading changed my life a lot.

    After learning art, rock climbing, and reading, now I've learnt that when we face difficulties, we should not give up. God closes a door for you, and will open another window for you.

示波器是电子技术实验测量中常用的仪器，若示波器中显象管的电子枪在2s内发6×10¹³个电子，则示波管中电流强度大小为         （  ）

如果下列四种粒子具有相同的速率，则德布罗意波长最大的是（　　）

昼夜更替，潮起潮落，地球自转运动产生了许许多多的自然现象。回答下列各题。

临床上根据病人病情需要，有针对性地选用不同的血液成分进行输血，对于贫血、大面积烧伤和血小板缺乏者，应分别输入（    ）