Answer the questions at the end based on the text.

Anti-aircraft warfare or counter-air defence is defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action." They include ground-and air-based weapon systems, associated sensor systems, command and control arrangements and passive measures (e.g. barrage balloons). It may be used to protect naval, ground, and air forces in any location. However, for most countries the main effort has tended to be 'homeland defence'. NATO refers to airborne air defence as counter-air and naval air defence as anti-aircraft warfare. Missile defence is an extension of air defence as are initiatives to adapt air defence to the task of intercepting any projectile in flight. 

Non-English terms for air defence include the German Flak (Fliegerabwehrkanone, "aircraft defence cannon", also cited as Flugabwehrkanone), whence English flak, and the Russian term Protivovozdushnaya oborona (Cyrillic: Противовозду́шная оборо́на), a literal translation of "anti-air defence", abbreviated as PVO. In Russian the AA systems are called zenitnye (i.e. "pointing to zenith") systems (guns, missiles etc.). In French, air defence is called DCA (Défense contre les aéronefs, "aéronef" being the generic term for all kind of airborne device (airplane, airship, balloon, missile, rocket, etc.)).

1. How is anti-aircraft or counter-air defence defined?
2. Who defined it?
3. How many things are included in that?
4. What is one of those things that is included?
5. What is the main efforts in most countries?
6. What do they call it in France?
7. What about in Germany?
8. What task do they have?
9. What are they referred to as in Russia?
10. How many examples are given as to what it is named in other places?

Numbered answers:
1. "all measures designed to nullify or reduce the effectiveness of hostile air action
2. NATO
3. Four
4. ground-and air-based weapon systems
5. homeland defence
6. DCA
7. Flak
8. intercepting any projectile in flight.
9. Protivovozdushnaya oborona
10. Four