Use the words given in the box to fill in the blanks

Use the words given in the box to fill in the blanks:
oil clean population energy decades important
As we know, ... increases and countries industrialize, the world's demand for ... increases. At the present time, gas and ... are expensive and petroleum suppiles are limited. So in a few ..., they will run out. However, the supply of sunlight is unlimited and it is also a ... source of energy. Scientists have proven that it can become an ... source of energy.
Unless scientists do research on solar energy, wind power, tidal waves, hydroelectric schemes, we'll all freeze or starve to death.