3．
Proper Care and Use of a Microscope
A microscope is a useful instrument for observing small objects．It shows people the details that are undetectable when they observe with their own eyes．Before using the microscope，please read the instruction below．
Caution：
Microscopes are both delicate and expensive，and must be handled with care．
1．Always carry the microscope with two hands-one supporting the base and the other on the arm．
2．Keep the stage clean and always use a glass slide for specimens，the things tested or examined．
3．To avoid pressing the glass slide when focusing，begin with the lens （镜头） close to the specimen and gradually back off to focus．
4．Keep the microscope covered to prevent the buildup of
dust while it is being stored．
How to Use the Microscope：
1．Plug in the lamp．
2．Place a specimen on a slide．
3．Adjust the mirror so it reflects light from the room up into the objective lens．
4．Place your slide with the specimen directly over the center of the glass circle on the stage．If it is a wet slide，be sure the bottom of the slide is dry．
5．With the LOW POWER objective lens placed over the slide，use the coarse focus knob to lower the lens to the lowest point．
6．Look through the eyepiece with one eye while closing the other eye．Slowly raise the lens until the focus is relatively clear．
7．Use the fine focus knob to make very small changes to the focus．
8．Without changing the focus knobs，switch to the HIGH POWER objective lens．Once you have
switched to HIGH POWER，use only the fine focus knob to make the image sharper．
56．When using a microscope，you should use a glass slide for specimens toA．
A．keep the stage clean
B．avoid pressing the lens
C．prevent the buildup of dust
D．support the base and the arm
57．When observing onion cells on a slide，which of the following should you do first？B
A．Lower the lens．
B．Adjust the mirror．
C．Turn the fine focus knob．
D．Look through the eyepiece．
58．What is the main purpose of this passage？C
A．To show the reader the various parts of a microscope．
B．To persuade the reader to buy this type of microscope．
C．To instruct the reader how to use a microscope with care．
D．To show the reader some advantages of using a microscope．
