Problem: A fundamental problem with software testing is that testing under all combinations of inputs and preconditions (initial state) is not feasible, even with a simple product.:17-18 This means that the number of defects in a software product can be very large and defects that occur infrequently are difficult to find in testing. More significantly, non-functional dimensions of quality (how it is supposed to be versus what it is supposed to do)usability, scalability, performance, compatibility, reliabilitycan be highly subjective; something that constitutes sufficient value to one person may be intolerable to another.
What other non-functional dimensions can cause software to underperform and cause other problems?
The answer is the following: usability, scalability, performance, compatibility, reliability

Problem: In addition, the city has about 160 museumsthe world's greatest single metropolitan concentration over 100 art galleries, and some 30 concert halls, all of which maintain a constant cultural activity during the whole year. It has either the third or fourth-highest number of theatres in the world after New York, London and perhaps Toronto. Many areas (e.g. Palacio Nacional and the National Institute of Cardiology) have murals painted by Diego Rivera. He and his wife Frida Kahlo lived in Coyoacan, where several of their homes, studios, and art collections are open to the public. The house where Leon Trotsky was initially granted asylum and finally murdered in 1940 is also in Coyoacan.
Who has painted murals all over the city?
The answer is the following: Diego Rivera

Problem: Besides increased efficiency of power plants, there was an increase in efficiency (between 1950 and 1973) of the railway utilization of this electricity with energy-intensity dropping from 218 to 124 kwh/10,000 gross tonne-km (of both passenger and freight trains) or a 43% drop. Since energy-intensity is the inverse of energy-efficiency it drops as efficiency goes up. But most of this 43% decrease in energy-intensity also benefited diesel traction. The conversion of wheel bearings from plain to roller, increase of train weight, converting single track lines to double track (or partially double track), and the elimination of obsolete 2-axle freight cars increased the energy-efficiency of all types of traction: electric, diesel, and steam. However, there remained a 1215% reduction of energy-intensity that only benefited electric traction (and not diesel). This was due to improvements in locomotives, more widespread use of regenerative braking (which in 1989 recycled 2.65% of the electric energy used for traction,) remote control of substations, better handling of the locomotive by the locomotive crew, and improvements in automation. Thus the overall efficiency of electric traction as compared to diesel more than doubled between 1950 and the mid-1970s in the Soviet Union. But after 1974 (thru 1980) there was no improvement in energy-intensity (wh/tonne-km) in part due to increasing speeds of passenger and freight trains.
What caused the energy efficiency to go up?
The answer is the following: energy-intensity dropping

Problem: The chemical composition of wood varies from species to species, but is approximately 50% carbon, 42% oxygen, 6% hydrogen, 1% nitrogen, and 1% other elements (mainly calcium, potassium, sodium, magnesium, iron, and manganese) by weight. Wood also contains sulfur, chlorine, silicon, phosphorus, and other elements in small quantity.
What element joins potassium, calcium, manganese, iron, and sodium to make a combined 1% of the chemical composition of wood?
The answer is the following:
magnesium