The word "proper" in the first line of the second paragraph means （）.

单项选择题It is mentioned in the passage that one has to pay tax according to （）.

A．how much education one has received
B．whether one is single or married
C．how old one's children are
D．where one lives

单项选择题According to the passage, to decide the exact amount of tax to be paid is （）.

A．simply
B．easy
C．difficult
D．interesting