SORU: aşağıdaki parçaya göre cevaplayınız
The passage tells us that today's oil, gas and coal ----.
Most of the power generated by mankind has its
origins in the sun. It was sunlight that nurtured the
early life that became today's oil, gas and coal. It is
the solar heating of the Earth's atmosphere and
oceans that fuels wave power, wind farms and
hydroelectric schemes. But using the sun's energy
directly to generate power is rare. Solar cells
account for less than 1% of the world's electricity
production. Recent technological improvements,
however, may boost this figure. The root of the
problem is that most commercial solar cells are
made from silicon, and silicon is expensive. Cells
can be made from other cheaper materials, but
these are not as efficient as those made from
silicon.