Problem: Printed circuit board:

Matte solder is usually fused to provide a better bonding surface or stripped to bare copper. Treatments, such as benzimidazolethiol, prevent surface oxidation of bare copper. The places to which components will be mounted are typically plated, because untreated bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was coated with solder by hot air solder levelling (HASL). The HASL finish prevents oxidation from the underlying copper, thereby guaranteeing a solderable surface. This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU and US, which restricts the use of lead. One of these lead-free compounds is SN100CL, made up of 99.3% tin, 0.7% copper, 0.05% nickel, and a nominal of 60ppm germanium.

What is now used in compliance with the RoHS directive in the EU and China?
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A: unanswerable

Problem: Houston's highway system has a hub-and-spoke freeway structure serviced by multiple loops. The innermost loop is Interstate 610, which encircles downtown, the medical center, and many core neighborhoods with around a 8-mile (13 km) diameter. Beltway 8 and its freeway core, the Sam Houston Tollway, form the middle loop at a diameter of roughly 23 miles (37 km). A proposed highway project, State Highway 99 (Grand Parkway), will form a third loop outside of Houston, totaling 180 miles in length and making an almost-complete circumference, with the exception of crossing the ship channel. As of June 2014, two of eleven segments of State Highway 99 have been completed to the west of Houston, and three northern segments, totaling 38 miles, are actively under construction and scheduled to open to traffic late in 2015. In addition to the Sam Houston Tollway loop mentioned above, the Harris County Toll Road Authority currently operates four spoke tollways: The Katy Managed Lanes of Interstate 10, the Hardy Toll Road, the Westpark Tollway, and the Fort Bend Parkway Extension. Other spoke roads either planned or under construction include Crosby Freeway, and the future Alvin Freeway.
What is the diameter of the center of Beltway 8?
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Answer: 23 miles

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Uniquely among major American cities, New York is divided between, and is host to the main branches of, two different US district courts: the District Court for the Southern District of New York, whose main courthouse is on Foley Square near City Hall in Manhattan and whose jurisdiction includes Manhattan and the Bronx, and the District Court for the Eastern District of New York, whose main courthouse is in Brooklyn and whose jurisdiction includes Brooklyn, Queens, and Staten Island. The US Court of Appeals for the Second Circuit and US Court of International Trade are also based in New York, also on Foley Square in Manhattan.
In what borough is the main courthouse of the District Court for the Southern District of New York located?
A: Manhattan

Context and question: Some biographical accounts include the autobiography Life on the Color Line: The True Story of a White Boy Who Discovered He Was Black by Gregory Howard Williams; One Drop: My Father's Hidden LifeA Story of Race and Family Secrets written by Bliss Broyard about her father Anatole Broyard; the documentary Colored White Boy about a white man in North Carolina who discovers that he is the descendant of a white plantation owner and a raped African slave; and the documentary on The Sanders Women of Shreveport, Louisiana.
What documentary features a black man in North Carolina?
Answer: unanswerable

Question: The density of paper ranges from 250 kg/m3 (16 lb/cu ft) for tissue paper to 1,500 kg/m3 (94 lb/cu ft) for some speciality paper. Printing paper is about 800 kg/m3 (50 lb/cu ft).
Is there an answer to this question: What is the common density of printing paper?

Answer: 800 kg/m3

Question: Vacuum is useful in a variety of processes and devices. Its first widespread use was in the incandescent light bulb to protect the filament from chemical degradation. The chemical inertness produced by a vacuum is also useful for electron beam welding, cold welding, vacuum packing and vacuum frying. Ultra-high vacuum is used in the study of atomically clean substrates, as only a very good vacuum preserves atomic-scale clean surfaces for a reasonably long time (on the order of minutes to days). High to ultra-high vacuum removes the obstruction of air, allowing particle beams to deposit or remove materials without contamination. This is the principle behind chemical vapor deposition, physical vapor deposition, and dry etching which are essential to the fabrication of semiconductors and optical coatings, and to surface science. The reduction of convection provides the thermal insulation of thermos bottles. Deep vacuum lowers the boiling point of liquids and promotes low temperature outgassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode ray tubes. The elimination of air friction is useful for flywheel energy storage and ultracentrifuges.
Is there an answer to this question: What are lightbulbs used to study?

Answer:
unanswerable