Computer Mouse Thebasic computer mouse is______(51)amazingly clever invention with a relativelysimple design that allows us to point at things on the computer and it is

veryproductive.Think of all the things you can do with a mouse like selecting textfor copying and pasting , drawing , and even scrolling（滚动）on the page with the newer

mice with thewheel.Most of us use the computer mouse daily without stopping to think howit______(52)until it gets dirty and we have to learn how to______(53)it.Welearn

to point atthings______(54)we learn to speak,so the mouse is a very natural pointingdevice.Other computer pointing devices include light pens,graphics tablets andtouch

screens,but themouse is still our workhorse. The computer mouse was_____(55)in 1964 by DouglasEnglehart of Stanford University.As computer screens became more

popalar and arrowkeys were used to move around a body of text,it became clear that a pointingdevice that allowed easier motion through the text and even selection of text

would be veryuseful.The introduction of the mouse,with the Apple lisa computer in1983,really started the computer public on the road to relying on themouse_____(56)

routine computertasks. How does the mouse work?We have to start at the bottom,so think upsidedown for now.It all starts with the mouse ball.As the mouse ball in the

bottom of the mouserolls over the mouse pad,it presses against and turns two shafts（轴）.The shafts are connected to wheelswith several small holes in them.The wheels

have a pair of smallelectronic light-emitting devices______(57) light-emitting diodes(LED)mountedon either side.One LED sends a light beam to the LED on______(58)

side.As the wheelsspin and a hole rotates by,the light beam gets through to the LED on the otherside.But a moment______(59)the light beam is blocked until the next hole is

in place.TheLED______(60)a changing pattern of light, converts the pattern______(61)anelectronic signal,and sends the signal to the computer through wires in a cablethat

goes out of themouse body.This cable is the tail that helps give the mouse its name.Thecomputer interprets the signal to tell it where to position the cursor on the

computer______(62).So far we have only discussed the basic computer mouse that______(63)of youprobably have or have used.One problem with this design is that the

mouse gets dirty asthe ball rolls over the surface and picks up dirt.______(64)you have to cleanyour mouse.The newer optical mice______(65)this problem by having no

moving parts.54._________

A.before

B.after

C.until

D.unless