In the following passage some of the words have been deleted. Read the passage carefully and select the correct answer for the given blank out of the four alternatives.

In Switzerland these glacial meltwater are (1)_______ for hydropower. In fact, water on 93% of Switzerland ultimately passes (2)______ at least one electric plant before even (3)__________ the country. So one consequence is that melting glaciers help to (4)_________ for low rainfall in times of drought, filling reservoirs to supply the nation's (5)______ supply.

Select the most appropriate option to fill in the blank no. 5.

energy

- In the sentence, " filling reservoirs to supply the nation's ______ supply.", the word energy is the most suitable.

- The whole passage is based on energy production in Switzerland. 

- The complete sentence becomes: " filling reservoirs to supply the nation's energy supply."