题目

How to keep screens from ruining your visionLaboratory studies have shown that prolonged exposure to high-intensity blue light damages retinal (视网膜的) cells in mice. But epidemiological (流行病学的) studies on real people tell a different story.So,【1】Human eyes are different from rodent (啮齿动物) eyes. We have protective elements, such as macular pigments and the natural blue-blocking ability of the crystalline lens (晶状体).【2】 Just because blue light isn’t harming your retina doesn’t mean your electronic devices are harmless. Because of its wavelength, blue li已知10件不同产品中共有4件次品,现对它们进行一一测试,直至找到所有次品为止.（1）若恰在第5次测试,才测试到第一件次品,第10次才找到最后一件次品的不同测试方法数有多少种?（2）若恰在第5次测试后,就找出了所有次品,则这样的不同测试方法数有多少种?