would you like to have a look at some trousers?they may fit

would you like to have a look at some trousers?they may fit you well.well,i'd like to...
would you like to have a look at some trousers?they may fit you well.
well,i'd like to try those blue _____.
A.pairs B.ones
这里为什么选A不选B?
可是one不是也有作特指和代词之类的形式么 比如which bag do you like?i like the red one.又如何呢？