Although we may think we are not affected by them, Dr. Krugman believes that advertisements affect （）.

单项选择题73（）

A．was   
B．is   
C．has been   
D．should be

单项选择题The author wrote a note of appreciation to the post office because （）.

A．he knew what such a note would mean to the post office
B．he had discovered giving-away made life more exciting
C．he believed he would get something back by doing so
D．the postman delivered an important letter in time