观察标本时，若光线太强，应将反光镜的______镜对准光源，同时光圈应调到______．
在显微镜的结构中，反光镜有两个面，平面镜和凹面镜，当光线强时用平面镜，因凹面镜起到汇聚光线的作用，光线弱时用凹面镜；在遮光器的下面有一些光圈，当光线强时用小光圈，光线弱时用大光圈．即：当外界光线较强时，选用的是小光圈和平面镜；外界光线较弱时，选用的是大光圈和凹面镜．
故答案为：平面；较小
| 完形填空 My name is Jane Eyre and my parents died when I was a baby. For ten years I lived a__1__life with my aunt and cousins who treated me unfairly. My cousins teased me and my aunt never showed me any__2__.The only person who cared about me was the maid, Bessie. One day my cousin John __3__me: "You should go and beg, not live with rich folks like us!" After fighting with him I was locked in a room, where I __4__for hours crying. Things __5__the same until a tall gentleman called Mr Brockehurst came to visit. My aunt told me that I was going to a school __6__by the gentleman. "Train her to be useful and humble," said Aunt. Two days later I __7__my home. At first my __8__at Lowood School was easy. The food was bad and I was often cold but I made __9__and enjoyed studying. But after an illness killed several students, new owners __10__the school and life improved. Six years later I __11__ a teacher and was very happy. But eventually(最后) I felt that I should explore more of the world and found a job as a private teacher in a __12__. Before I left Lowood, I was__13__by Bessie, who told me that seven years ago my father's brother had come __14__me but left again to go abroad. "He looked like quite a gentleman," said Bessie. I wondered if he would ever look for me again. My new life __15__at Thornfield Hall, a large country house, __16__a little girl called Adele. She was the adopted(被收养的) daughter of the owner of the house, Mr Rochester. He __17__stayed at Thornfield and __18__my time was mainly spent with Adele and the servants. My life was quite happy now although there was something__19__about my new home. Often I heard odd(奇怪的) sounds __20__from the top floor of the house. | ||||
|