1. what is the author’s main thesis (argument) in setting up his book? why/how are these fluids “vital”?

The author, Tom Standage, argues that deliberately-made beverages represent a variety of roles and commemorations to their respective societies and world history. He believes that these beverages symbolize the time periods, cultures, and achievements of their respective eras.

Standage asserts that the six fluids of beer, wine, spirits, tea, coffee, and Cocoa Cola are vital to understanding the histories of, " ... agriculture, philosophy, religion, medicine, technology, and commerce ..."

your answer would be (b)