There is------blue T-shirt on the table.whose is this?

There is______blue T-shirt on the table.whose is this?
It's mine.
A a B the
答案是A为什么呢?怎样区分好冠词的用法
You love to play chess,don‘t you?
_____I prefer to play chess.
A YES,I do B NO,I don't
错了，应该是prefer to play tennis
可是第一个不是特指的某个事物吗？