You can add any number of adjectives, in theory, as you wish. But just follow the rule of SACOM, ie, size/shape - age - colour - origin - materials, and any other adjectives can be put in the front. But for your example -- 'a pretty smart guy', the word 'pretty' is an adverb, it describe the degree of 'smart' of the guy. THIS IS NOT AN EXAMPLE FOR MULTIPLE ADJECTIVES USE!! 理论上,你可以加无限多的形容词。但要遵守SACOM规则,即:大小形状最先(size/shape)-新旧年龄(age)-颜色(colour)-来源(origin)-材料最后(materials),其他的形容词可以放在最前面。但你的例子—— ‘a pretty smart guy’ 中的 ‘pretty’ 是副词,它用以修饰 ‘smart’ 这个形容词,也就是说,‘pretty’ 告诉我们那个guy有多么的 ‘smart’ 。这并不是形容词连用的例子!!!