One  major difference __13__ growing up in the city and in the country is the degree of friendliness. In large cities, we often hear of people living in huge apartment buildings with __14__ strangers. These urban apartment dwellers tend to be wary of unknown faces and rarely get to know their neighbors well. The situation in a small town is often just __15__. Small-town people generally grow up together, attend the same schools, and share the same friends. __16__, rural people are much more likely to treat their neighbors like family and invite them into their homes.

       Ocean waves represent our planet’s last untapped large-scale renewable energy resource. Over 70 % of the earth’s surface is covered with water. The energy contained within waves has the potential to produce up to 80,000 TWh (10¹² watt-hours) of electricity per year—sufficient to meet our global energy demand five times over.

       No wonder the idea of extracting energy from ocean waves and turning it into electricity is an alluring one. The first serious attempt to do so dates back to 1974, when Stephen Salter of Edinburgh University came up with the idea of “ducks”: house-sized buoys tethered to the sea floor that would convert the swell into rotational motion to drive generators. It failed, as have many subsequent efforts to perform the trick. But the idea of wave power will not go away, and the latest attempt—the brainchild of researchers at Oscilla Power, a firm based in Seattle—is trying to address head-on the reason why previous efforts have foundered.

       This reason, according to Rahul Shendure, the firm’s boss, is that those efforts took technologies developed for landlubbers (often as components of wind turbines) and tried to modify them for marine use. The consequence was kit too complicated and sensitive for the rough-and-tumble of life on the ocean waves, and also too vulnerable to corrosion. Better, he reckons, to start from scratch.

       Instead of generators with lots of moving parts, Oscilla is developing ones that barely move at all. These employ a little-explored phenomenon called magnetostriction, in which ferromagnetic materials (things like iron, which can be magnetized strongly) change their shape slightly in the presence of a magnetic field. Like many physical processes, this also works in reverse. Apply stresses or strains to such a material and its magnetic characteristics alter. Do this in the presence of permanent magnets and a coil of wire, such as are found in conventional generators, and it will generate electricity.