如何使用vbscript创建动态验证码

What generally occurs in the captcha's is that a single word is displayed and the user has to just enter that word in to validate the captcha. But in this case what I want is that my captcha would consist of a slogan(that is a sentence),and on each time the computer would ask like... Enter the first word in the slogan.. Next time it asks,Enter the third word and so on randomly... Can anyone provide me an idea how t d this?What generally occurs in the captcha's is that