B 自然常识用一般现在时+water是不可数 所以要单三 ..答案好像是C一般现在时表达客观真理，格言警句或事实 eg. The earth moves round the sun. 地球绕着太阳转。The sun rises in the east and sets in the west. 太阳东升西落。Two and two makes four. 二加二等于四。Seeing is believing. 眼见为实。