Title: Age of Enlightenment.
Question: Which century is considered by some as a "drab" period, however saw significant advancements in the practice of medicine, mathematics, and physics, the development of biological taxonomy, a new understanding of magnetism, and the maturation of chemistry as a discipline?

Title: BeiDou Navigation Satellite System.
Question: When was the second satellite for the BeiDou-2 system launched?

Title: Law of the United States.
Question: Some federal and state statutes remain on the books for how long after they are ruled unconstitutional?

Title: Red.
Question:
In which century did Saint Valentine's day become connected with lovers?