单项选择题 We can learn from the beginning of the text that doctors in Philadelphia（）

问答题 Directions: Suppose you are the secretary of the principal of your university. You are expected to write a memo to remind the principal of an important international meeting he has to attend the next day. Imagine some detailed activities the principal has to perform in the meeting. Write your memo in no less than 100 words. Write it neatly on ANSWER SHEET 2. Do not sign your own name on the memo; use Li Hua instead. Do not write the address. (10 points)

单项选择题 The author mentions increased installment debt in the first paragraph in order to show（）