A gradual agricultural revolution in northern Europe stemmed from concerns over food supplies at a time of rising populations.
北欧渐进的农业革命源于人口增长时期对粮食供应的担忧。
2
All existing supplies of helium ought to be conserved and released only by permit, with medical uses receiving precedence over other commercial or recreational demands.
Firstly, all existing supplies of helium ought to be conserved and released only by permit, with medical uses receiving precedence over other commercial or recreational demands.