艾伦的脸皱了起来，好像要打喷嚏。Ellen's face wrinkles as if she is about to sneeze.打喷嚏的时候眼睛会闭上。When we sneeze, our eyes close.我们打喷嚏究竟是怎么回事？What exactly happens when we sneeze?...
Lead was one of the metals known to the ancient world.铅是早在古代就已知的金属之一。Metals expand when they are heated.金属受热会膨胀。What spurred them on was alchemy, the'science " of changing ordinary metals into gold.激励他们的是炼金术, 即把普通金属...