天文学家能够测定每颗恒星的亮度。An astronomer can determine the brightness of each star.这颗恒星的表面温度估计在零下75摄氏度左右。The star's surface temperature is reckoned to be minus 75 degrees Celsius.这些恒星一定是形成于100到150亿年前。The stars must have formed...
牛的口蹄疫能被无细菌的滤液传播.Food - and - mouth disease of cattle could be transmitted by bacteria - free filtrates.口蹄 疫 已传播到爱尔兰 、 法国、荷兰, 可能还有德国.Foot - and - mouth disease has already spread to Ireland, France and the Netherlands, an...