参考答案：C

解析： 动词辨析。
roll(使某物)滚动：The ball rolled down the hill．球滚下了山。cascade(使)瀑布般地落下：Her golden hair cascaded down her back．她的金发像瀑布似的披在背后。cast投，抛：The angler cast the line．垂钓者把钓线抛了出去。caste社会等级，社会地位(名词)：The caste system is still strong in some Eastern countries such as India．种姓制度在一些东方国家如印度仍然很牢固。cataract(使)像瀑布似地注流：The rotor cataracts water over the top of the machines．回转轮将水从机器顶上注入。