What is the principle of federalism?

It's where the federal government and many state governments share power. Or in other words, power is divided between federal and state. Because of this system power cannot be abused! 

Hope this helps!

The answer should be b.

Tenochtitlán was the capital of the aztec empire. it was a busy and bustling city where“there are daily more than 60,000 souls, buying and selling, and where are found all the kinds of merchandise produced in these countries.” when cortes arrived in 1519, theenormity of the trading market and the smoothness of it’s running both surprised and  impressed him.