Misc: During World War II, what were U-Boats?

Questions

In the 9th century which city had several thousand bookstores?

In the Gregorian calendar after 10,000 years by how many days will the calendar be wrong by?

In the kama-sutra the art of which game is recommened for women to study?

In the period 978-1016 England was ruled by which "Unready" king?

In the year 2000 which companies CEO was the worlds second richest man?