Title: Glass.
Question: The thickness at the bottom of glass panes was once taken as evidence that glass had features of what state of matter?

Title: Tucson, Arizona.
Question: What drug company has a major presence in Tucson?

Title: Military history of the United States.
Question: Prior to the Persian Gulf War, where and when was the last major American military conflict?

Title: Bird.
Question:
What is the number range of living bird species?