阅读理解 Many adults may think they're getting enough shut-eye, but in a major sleep study almost 80 percent of respondents admitted to not getting their prescribed amount of nightly rest. Research shows that adults need an average of seven to nine hours of sleep a night for optimal functionality.
By getting less than six hours of sleep a night, you put yourself at risk for high blood pressure. When you sleep, your heart gets a break and slows down for a significant period of time. But cutting back on sleep means your heart has to work overtime without its allotted break. In constantly doing so, your body must accommodate to its new conditions and elevate your overall daily blood pressure. And the heart isn't the only organ that is overtaxed by a lack of sleep. The less sleep you get, the less time the brain has to regulate stress hormones, and over time, sleep deprivation could permanently hinder the brain's ability to regulate these hormones, leading to elevated blood pressure.
Prolonged sleep deprivation has long been associated with diminished immune functions, but researchers have also found a direct correlation between "modest" sleep deprivation—less than six hours—and reduced immune response.
During deep REM sleep, your muscles (except those in the eyes) are essentially immobilized in order to keep you from acting out on your dreams. Unfortunately, this effort your body makes to keep you safe while dreaming can sometimes backfire, resulting in sleep paralysis. Sleep paralysis occurs when the brain is aroused from its RMR cycle, but the body remains in its immobilizing state. This can be quite a frightening sensation because, while your mind is slowly regaining consciousness, it has no control over your body, leaving some with a feeling of powerlessness, fear and panic.
Imagine all of your memories are erased. It's a chilling thought, but that is what a life without sleep would be like. Sleep is essential to the cognitive functions of brain, and without it, our ability to consolidate memories, learn daily tasks, and make decisions is impaired by a large degree. Research has revealed that REM sleep, or dream-sleep, helps solidify the "fragile" memories the brain creates throughout the day so that they can be easily organized and stored in the mind's long-term cache.

【正确答案】 B

【答案解析】第四段第一句说，在快速眼动睡眠(REM)的时候，除了眼睛上的肌肉以外，你全身的肌肉基本上都是不动的，这是为了让你在做梦时不会肢体乱动(以免弄伤自己)。紧接着第二句，用unfortunately进行转折：你全身肌肉不动是为了保护你睡眠的安全，可有时也会backfire，即引起“睡眠瘫痪”。根据上下文的逻辑，可以看出backfire的意思是选项[B]，即产生事与愿违的结果。