因为slow 本身就可以做副词,和slowly没什么区别
副词可以修饰副词 too...to可以修饰副词 楼上的回答都不对
但是 ：由特殊 的 请看下面:
slow,slowly；quick,quickly等等异形同义词.当 然,现代英语的语言规范性要求 用以-ly 结尾的副词来修饰动词,但由于句子 结构以及搭配的不同,使用时也具有不同的倾向性.在此,主要 探讨一下在什 么情况下常使用不带-ly的副词形式.
Ⅰ 用作比较级或最高级时：
1.Allen was walking quickly,but George was walking evenquicker.艾伦走得很快,但乔治走得更快 .
2.The men were quarreling loudly,but the policemenshouted louder.那些人在大声争吵着,但 是警察喊叫得更响.
3.The car went slower and slower until it came to a stand still.汽车走得越来越慢,最后停了下 来.
4.Let's see who can run quickest.我们来看看谁跑得最快.
5.We must look closer at the problem.我们必须更加仔细地查看这一问
题.
Ⅱ 有"so"或"too"修饰时：
1.It all happened so quick that I could do nothing.这一切发生得如 此之快以致于我手足无措无
法 对付了.
2.It is impossible to overtake him; your car goes tooslow.不可能赶 上他了,你的车太慢了.
3.Don't talk so loud; the child is in bed now.别这样大声说话,孩子 已经睡了.
Ⅲ 用于修饰表示移动、天气等常用动词时：
1.Come quick; we are waiting for you.快来,我们在等你.
2.Drive slow; this part of the road is dangerous.车开慢一点,这段 路很危险.
3.The sun shines bright.阳光明媚.
4.When we left the shelter,the snow was falling thickand the wind was blowing cold.我们 离开那棚屋时,正下着大雪,刮着寒风.
5.Business is going strong.生意兴隆.
Ⅳ 在固定词组中或当用于修饰它经常固定搭配的动词时：
1.Take it easy.不要紧张.
2.Stand firm and hold it tight.站稳抓牢.
3.He often plays high.他赌注常下得很大.
4.The secretary copied the rough draft of her manager outfair.秘书 把经理那份粗潦的草稿很清 楚地誊写出来.
5.They were drinking deep in the fort deep into the night.他们在城 堡中痛饮到深夜.
