Article: In general relativity, a vanishing stress-energy tensor implies, through Einstein field equations, the vanishing of all the components of the Ricci tensor. Vacuum does not mean that the curvature of space-time is necessarily flat: the gravitational field can still produce curvature in a vacuum in the form of tidal forces and gravitational waves (technically, these phenomena are the components of the Weyl tensor). The black hole (with zero electric charge) is an elegant example of a region completely "filled" with vacuum, but still showing a strong curvature.

Question: What has no electric charge?
Ans: black hole

Article: Kouros (male youth) is the modern term given to those representations of standing male youths which first appear in the archaic period in Greece. This type served certain religious needs and was first proposed for what was previously thought to be depictions of Apollo. The first statues are certainly still and formal. The formality of their stance seems to be related with the Egyptian precedent, but it was accepted for a good reason. The sculptors had a clear idea of what a young man is, and embodied the archaic smile of good manners, the firm and springy step, the balance of the body, dignity, and youthful happiness. When they tried to depict the most abiding qualities of men, it was because men had common roots with the unchanging gods. The adoption of a standard recognizable type for a long time, is probably because nature gives preference in survival of a type which has long be adopted by the climatic conditions, and also due to the general Greek belief that nature expresses itself in ideal forms that can be imagined and represented. These forms expressed immortality. Apollo was the immortal god of ideal balance and order. His shrine in Delphi, that he shared in winter with Dionysius had the inscriptions: (gnothi seauton="know thyself") and (meden agan, "nothing in excess"), and ' (eggya para d'ate, "make a pledge and mischief is nigh").

Question: What is another word for male youth?
Ans: Kouros

Article: After Cao's defeat at the naval Battle of Red Cliffs in 208 AD, China was divided into three spheres of influence, with Cao Cao dominating the north, Sun Quan (182252 AD) dominating the south, and Liu Bei (161223 AD) dominating the west. Cao Cao died in March 220 AD. By December his son Cao Pi (187226 AD) had Emperor Xian relinquish the throne to him and is known posthumously as Emperor Wen of Wei. This formally ended the Han dynasty and initiated an age of conflict between three states: Cao Wei, Eastern Wu, and Shu Han.

Question: Who was in control of the south of China?
Ans: Sun Quan

Article: In 1870, following the stunning defeat of the French Army by the Germans in the Franco-Prussian War, French workers and socialist revolutionaries seized Paris and created the Paris Commune. The Commune lasted for two months before it was crushed by the French Army, with much bloodshed. The original red banners of the Commune became icons of the socialist revolution; in 1921 members of the French Communist Party came to Moscow and presented the new Soviet government with one of the original Commune banners; it was placed (and is still in place) in the tomb of Vladimir Lenin, next to his open coffin.

Question: In what year did people of the French Communist party go to Moscow to give the Soviet government a Paris Commune banner?
Ans:
1921