你可以简化一下句子就容易理解了to me 对句子语法没影响 省掉 就成了this means that which is planted must be revisited oftenwhich应改成what 如果用which的话就少成分了这句子 which是疑问代词 那它替代什么呢?也就是没有先行词 所以不能用which引导定语从句用what疑问副词就可以解释得通了 what在这里引导主语从句 what is planted 在what is planted must be revisited often中作主语...