问题 选择题

在“观察洋葱表皮细胞”实验中,将低倍镜换成高倍镜观察时,发现视野太暗,为增加视野亮度,下列操作合理的是(  )

A.移动装片

B.调节粗准焦螺旋

C.增大光圈

D.调节细准焦螺旋

答案

外界光线进入显微镜的路线是:反光镜→遮光器上的光圈→物镜→镜筒→目镜→眼睛;反光镜有两个面,分别称为平面镜和凹面镜,根据光线的强弱选用,遮光器上的小孔称为光圈,能够控制进入镜筒的光量.因此在显微镜的结构中,能够调节视野亮度的是遮光器和反光镜,遮光器上的大光圈和凹面镜可以增加显微镜视野的亮度.

如果由低倍物镜转换成高倍物镜后,视野中的物像进一步被放大,进入视野中的光线相应地减少,所以会现视野亮度变暗,为增加视野亮度,可增大光圈.

故选:C.

阅读理解

On some level, I always knew that I wanted to be a doctor-at least from the age of eight or ten years old, anyway.

Although my father wasn’t a doctor, he made his own brand of “house calls”. I followed him as he brought a plate of my mother’s home cooking to an elderly man named Frank on all major holidays and when Frank was sick. As far as I know, their only connection was that Frank was an occasional customer at Dad’s small gas station. Frank’s home was a two-room house on the rough side of town with an old front porch (门廊) where you could fall if you weren’t careful. Frank had no relatives and as far as I could tell, no other visitors either. Through his attitude and by caring, my father was teaching me to be a doctor, although neither of us knew it at the time.

When I was 13, my father developed lung cancer. He brought home a diagram the doctor had drawn showing where his cancer was and told me that he was going to die. He asked me to take care of my mother when he was gone. I was an only child. He said he loved me on the night when he died.

When you’re 13 and your father dies, you have some choices to make. You can use the situation as an excuse for letting your actions and graded go down, or you can honor his memory and try to do something positive with yourself. I focused my energy on my schoolwork and my goal of becoming a doctor.

1. What’s the father’s “own brand of ‘house calls’”?

A. his treatment for frank’s serious illness.

B. his care for Frank.

C. his attitude towards the author.

D. his wish that his kid would be a doctor.

2. The author began to want to be a doctor when_________

A. father helped frank regularly   

B. Father developed lung cancer

C. father asked him/her to take care of Mother   

D. father died

3. what was the influence of Father’s death on the author?

A. The author began to think seriously about his/her career.

B. The author was too sorrowful to carry through his /her study.

C. The author used the situation as an excuse for quitting school.

D. The author made great effort at his/her goal of becoming a doctor.

4. The best title for the text would be_________.

A. What Made Father Respectable

B. What Led Me to Be a Doctor

C. How to Help Strangers    

D. How to Deal with Death

判断题