Do you object to drinking black tea , Mr.Zhang ?
neutral
user
Yes , that is why I never drink it .
neutral
assistant
Do you drink green tea , then ?
neutral
user
Very seldom , because tea has tannin which may be harmful to one's health .
neutral
assistant
But if the tea is good and well prepared , it will do much good .
neutral
user
What good is it for ?
neutral
assistant
Not only can it appease one's thirst , but it can also refresh one when tired .
neutral
user
That's true , but it must not be allowed to stand long .
neutral
assistant
Why is it so ?
neutral
user
Because if you drink a kind of tea which has been prepared for some time before , it will do you harm .
neutral
assistant