One of the main sources of revenue for many states is
a. a poll tax placed on voter registrations.
b. a sales tax placed on goods and services. c.a duty on products exported from the state. d.a tariff on products imported from other states.

The correct answer for this question is "C.a duty on products exported from the state." One of the main sources of revenue for many states is a duty on products exported from the state. Revenue by definition refers to the income that a business has from its normal business activities. It may come from the sale of goods and services to customers. 

Joke: i thought it said drake and josh at first answer: probably unsure about this law. depending on how long the time is.