The cities of new york, baltimore and philadelphia began to become wealthy in the late 1600s because of what economic activity

This question is incomplete, here´s the complete question.  

The cities of New York, Baltimore, and Philadelphia began to become wealthy in the late-1600s because of what economic activity?

A) trading

B) slavery

C) rice farming

D) tobacco farming

A) trading

Explanation:

British Mercantilism was a key element for the colonial cities in the United States to prosper. The biggest cities took an especific economic role in the trade with Europe. While New York most important trade were flours and furs, Philadelphia traded on meat, wheat, and lumber,  and Baltimore eventually prospered by developing the flour-exporting trade.

500 books can be produced by one man and a printing press within 5 months, while a copyist can only produce one in the same amount of time

basic principles: federalism, separation of powers, checks and balances, judicial review, representative democracy, limited government, rule of law, individual rights and responsibilities, consent of the governed, majority rule, popular sovereignty, equal protection.