31.   The country is diversifying its energy sources.

32.   The environmental activist eagerly launched into an explanation of the hows and whys of developing renewable energy sources.

33.   Might the modulation of pulsars or the energy source of quasars,for example,have a technological origin?

34.   The Swedish government announced in mid-January that it would delay a promised phase-out of nuclear power until alternative energy sources became viable.

35.   Renewable energy sources replenish themselves naturally in a relatively short space of time.

36.   An energy source which could potentially supply up to ten times our energy needs for several thousand years is called an indefinitely sustainable energy source.

37.   Such energy sources include nuclear fission, nuclear fusion, solar energy together with biomass, controlled thermonuclear fusion and, finally, geothermal energy.

38.   These are sources of energy that are currently being developed to replace conventional energy sources.

39.   The most important are nuclear fission, wind, wave and tidal energy sources and solar energy by direct conversion and biomass.

40.   The primary energy source of industrialised countries has always been fossil fuels.