Problem: BeiDou Navigation Satellite System:

The ranging signals are based on the CDMA principle and have complex structure typical of Galileo or modernized GPS. Similar to the other GNSS, there will be two levels of positioning service: open and restricted (military). The public service shall be available globally to general users. When all the currently planned GNSS systems are deployed, the users will benefit from the use of a total constellation of 75+ satellites, which will significantly improve all the aspects of positioning, especially availability of the signals in so-called urban canyons. The general designer of the COMPASS navigation system is Sun Jiadong, who is also the general designer of its predecessor, the original BeiDou navigation system.

What are the ranging signals of the BeiDou system based on?
---
A: the CDMA principle


Problem: Washington University has a large number of student-run musical groups on campus, including 12 official a cappella groups. The Pikers, an all-male group, is the oldest such group on campus. The Greenleafs, an all-female group is the oldest (and only) female group on campus. The Mosaic Whispers, founded in 1991, is the oldest co-ed group on campus. They have produced 9 albums and have appeared on a number of compilation albums, including Ben Folds' Ben Folds Presents: University A Cappella! The Amateurs, who also appeared on this album, is another co-ed a cappella group on campus, founded in 1991. They have recorded seven albums and toured extensively. After Dark is a co-ed a cappella group founded in 2001. It has released three albums and has won several Contemporary A Capella Recording (CARA) awards. In 2008 the group performed on MSNBC during coverage of the vice presidential debate with specially written songs about Joe Biden and Sarah Palin. The Ghost Lights, founded in 2010, is the campus's newest and only Broadway, Movies, and Television soundtrack group. They have performed multiple philanthropic concerts in the greater St. Louis area and were honored in November 2010 with the opportunity to perform for Nobel Laureate Douglass North at his birthday celebration.
What is the name of the oldest a cappella group at Washington University?
---
Answer: The Pikers


Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
DEC operating systems (OS/8, RT-11, RSX-11, RSTS, TOPS-10, etc.) used both characters to mark the end of a line so that the console device (originally Teletype machines) would work. By the time so-called "glass TTYs" (later called CRTs or terminals) came along, the convention was so well established that backward compatibility necessitated continuing the convention. When Gary Kildall cloned RT-11 to create CP/M he followed established DEC convention. Until the introduction of PC DOS in 1981, IBM had no hand in this because their 1970s operating systems used EBCDIC instead of ASCII and they were oriented toward punch-card input and line printer output on which the concept of carriage return was meaningless. IBM's PC DOS (also marketed as MS-DOS by Microsoft) inherited the convention by virtue of being a clone of CP/M, and Windows inherited it from MS-DOS.
What did Gary Klidall clone to create PC DOS?
A: unanswerable


Context and question: United Nations' Secretary-General Ban Ki-moon has said that "renewable energy has the ability to lift the poorest nations to new levels of prosperity". In October 2011, he "announced the creation of a high-level group to drum up support for energy access, energy efficiency and greater use of renewable energy. The group is to be co-chaired by Kandeh Yumkella, the chair of UN Energy and director general of the UN Industrial Development Organisation, and Charles Holliday, chairman of Bank of America".
 Who is chair of US Energy?
Answer: unanswerable


Question: Chopin's public popularity as a virtuoso began to wane, as did the number of his pupils, and this, together with the political strife and instability of the time, caused him to struggle financially. In February 1848, with the cellist Auguste Franchomme, he gave his last Paris concert, which included three movements of the Cello Sonata Op. 65.
Is there an answer to this question: Who did Chopin have at his last Parisian concert in 1848?

Answer: Auguste Franchomme


Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Everton regularly take large numbers away from home both domestically and in European fixtures. The club implements a loyalty points scheme offering the first opportunity to purchase away tickets to season ticket holders who have attended the most away matches. Everton often sell out the full allocation in away grounds and tickets sell particularly well for North West England away matches. In October 2009, Everton took 7,000 travelling fans to Benfica, their largest ever away crowd in Europe since the 1985 European Cup Winners' Cup Final.
How many travelling fans did Everton bring with them to Benefica in 2009?
A:
7,000