Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

The .......... of energy in India are met from both commercial and non-commercial sources. The most .......... sources of energy today are coal and natural gas, hydro electricity and nuclear power. On the other hand, firewood, cow-dung cakes and vegetable waste etc...................non commercial forms of energy. While non-commerical forms of energy.........demand, coal is the ...........source of commercial energy in India.

On the other hand, firewood, cow-dung cakes and vegetable waste etc. _____ non commercial forms of energy.

• constitues

• combines

• mixes

• collaborates