It cannot be used as a sustainable source of differentiation.

Most sites have not yet found a sustainable source of revenue.

Look more closely and you will see that much of it comes from sustainable sources.

Pity the 'global economy' isn't putting the same effort into developing more sustainable sources of energy.

It will take the pressure off the need to research sustainable and renewable sources of energy.

"That is not a sustainable source of demand," he said.

Nuclear power is not a sustainable source of energy.

We must change over quickly to sustainable sources so that the generations to come will not be faced with a crisis.

Nuclear power cannot be a sustainable source of energy.

Research into energy should take place in the areas where sustainable sources of energy can be developed.