every few years,the coal workers have their lungs X-rayed to ensure their health 为什么不选have had
问题描述：
every few years,the coal workers have their lungs X-rayed to ensure their health 为什么不选have had
every few years不是现在完成时的标志吗
答
“每隔几年”,不是现在完成时的标志.
现在完成时要么表示已经完成的动作；要么表示过去发生的动作对现在的影响.
在这句话中“矿工每隔几年就要做肺部的X光检查以确保身体的健康”,很显然,矿工们过去在检查,几年后还要做检查,现在做,以后还要做,用一般现在时就能表示出这一现象,并不涉及完成时.