Both state governments and the federal government have the power to A. negotiate treaties.
B. regulate interstate trade.
C. collect taxes.
D. issue state licenses

c.

Explanation:

because because they both have the power to collect taxes

porter is writing economic history because he is focusing on the cost of developing vaccines.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).