American English has so many dfialects because people have come from all over the world.（people have come from 为什么要用have
问题描述：
American English has so many dfialects because people have come from all over the world.（people have come from 为什么要用have这个现在完成时态 能说 because people come from all over the world)
答
这个问题还真不太清楚.
从语法上讲,改为一般现在时是没有错误的；也许是习惯问题