I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Many of Tesla's writings are freely available on the web, including the article "The Problem of Increasing Human Energy," published in The Century Magazine in 1900, and the article "Experiments With Alternate Currents Of High Potential And High Frequency," published in his book Inventions, Researches and Writings of Nikola Tesla."? 

A book is full of?