Little主 is known谓 about the causes of exercise injuries状. 人们对运动损伤的原因知之甚少。这是一个否定句。被动语态。主语是little,是个代词,意思是“几乎没有”变为主动就是:People know little about the causes of exercise injuries人们对运动损伤的原因知之甚少。又如:However,little is known about his stay in Europe. Little is known of the marine animals that live in total darkness in the deepest part ofAtlantic. 对于生活在完全黑暗的大西洋深处的海洋动物,我们的了解是非常之少的。