A、Theyare caused by great temperature differences between adjacent air masses. There are four major jet streams.
B、Sincethe progress of an airplane is aided or impeded depending on whether tail windsorhead winds are encountered.
C、Insteadof moving along a straight line, the jet stream flows in a wavelike fashion;the wavespropagate eastward (in the Northern Hemisphere) at speeds considerably slower than the wind speed itself.
D、Jetstream, narrow, swift currents or tubes of air found at heights ranging from 7to 8 mi(11.3–12.9 km) above the surface of the earth.
E、In the Northern Hemisphere the jet stream issought by eastbound aircraft, in order to gain speed and savefuel, and avoided by westbound aircraft.
Theco-evolutionary relationship between cows and grass is one of nature'sunderappreciated wonders; it also happens to be the key to understanding justabout everything about modern meat.
For the grasses,which have evolved to withstand the grazing of ruminants, the cow maintains andexpands their habitat by preventing trees and shrubs from gaining a foothold andhogging the sunlight; the animal also spreads grass seed, plants it with hishooves, and then fertilizes it with his manure.
In exchange for these services the grasses offerruminants a plentiful and exclusive supply of lunch. For cows (like sheep, bison,and other ruminants) have evolved the special ability to convert grass— whichsingle-stomached creatures like us can't digest—into high-quality protein. Theycan do this because they possess what is surely the most highly evolveddigestive organ in nature: the rumen. About the size of a medicine ball, theorgan is essentially a forty-five-gallon fermentation tank in which a residentpopulation of bacteria dines on grass.