now there are already robots working in factories .为什么用working 而不是work
问题描述：
now there are already robots working in factories .为什么用working 而不是work
答
因为前面已经有are和now代表它的时态为现在进行时,故使用working而不是work那today there are already robots working in factories 呢？同理，today也是用于现在进行时货或一般现在时，但后面有了are，所以为进行时