题目内容：
根据下面资料，回答题 Problems Caused by Using Computers
Long hours at the screen can cause 41 (ache) eyes, 42 (blur) vision and headaches,experts say. In fact, eyestrain surpasses even wrist pain as the top physical 43 (complain) amongheavy computer users. When peering into the computer screen, the eye' s focusing muscle is at constant tension. Like any muscle,it feels sore when 44 (overload). And when someone spends a lot
of time looking at something close, the eye muscle can get 45 (stick) on the near-focus settingand have difficulty relaxing, leaving the person 46 (temporary) nearsighted, a condition calledaccommodative spasm (痉挛) that can last seconds or hours. The letters on the screen are not asclearly 47 (define) as on a printed page. Take a magnifying glass to your monitor and you' ll see
the letters,each made up of pinpoint sources of light, have no sharp edges. But those liquid crystaldisplay (LCD) monitors, like those found on laptop computers, are 48 (easy) on the eyes because they display sharper images. And studies have shown that when people are working on a computer,their rate of 49 (blink) goes down by two-thirds, which can result in dry, stinging eyes.
This is especially a problem for contact-lenses 50 (wear).
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