Question: The just-noticeable difference (jnd) (the threshold at which a change is perceived) depends on the tone's frequency content. Below 500 Hz, the jnd is about 3 Hz for sine waves, and 1 Hz for complex tones; above 1000 Hz, the jnd for sine waves is about 0.6% (about 10 cents). The jnd is typically tested by playing two tones in quick succession with the listener asked if there was a difference in their pitches. The jnd becomes smaller if the two tones are played simultaneously as the listener is then able to discern beat frequencies. The total number of perceptible pitch steps in the range of human hearing is about 1,400; the total number of notes in the equal-tempered scale, from 16 to 16,000 Hz, is 120.
Try to answer this question if possible: The just-noticeable difference, at which a change is perceived depends on what?
Answer: the tone's frequency content
Question: Nutritional anthropology is a synthetic concept that deals with the interplay between economic systems, nutritional status and food security, and how changes in the former affect the latter. If economic and environmental changes in a community affect access to food, food security, and dietary health, then this interplay between culture and biology is in turn connected to broader historical and economic trends associated with globalization. Nutritional status affects overall health status, work performance potential, and the overall potential for economic development (either in terms of human development or traditional western models) for any given group of people.
Try to answer this question if possible: Nutritional anthropologists investigate the interplay between economic systems and what?
Answer: food security
Question: Unlike the American GPS, Russian GLONASS, and European Galileo systems, which use medium Earth orbit satellites, BeiDou-1 uses satellites in geostationary orbit. This means that the system does not require a large constellation of satellites, but it also limits the coverage to areas on Earth where the satellites are visible. The area that can be serviced is from longitude 70°E to 140°E and from latitude 5°N to 55°N. A frequency of the system is 2491.75 MHz.
Try to answer this question if possible: BeiDou-1, along with European Galileo systems, use which type of satellites? 
Answer: unanswerable
Question: While the use of iron started to become more widespread around 1200 BC, mainly because of interruptions in the trade routes for tin, the metal is much softer than bronze. However, very small amounts of steel, (an alloy of iron and around 1% carbon), was always a byproduct of the bloomery process. The ability to modify the hardness of steel by heat treatment had been known since 1100 BC, and the rare material was valued for the manufacture of tools and weapons. Because the ancients could not produce temperatures high enough to melt iron fully, the production of steel in decent quantities did not occur until the introduction of blister steel during the Middle Ages. This method introduced carbon by heating wrought iron in charcoal for long periods of time, but the penetration of carbon was not very deep, so the alloy was not homogeneous. In 1740, Benjamin Huntsman began melting blister steel in a crucible to even out the carbon content, creating the first process for the mass production of tool steel. Huntsman's process was used for manufacturing tool steel until the early 1900s.
Try to answer this question if possible: Heat treatment of steel has been know since what time?
Answer:
1100 BC