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. 1.

used 

- In the first blank,"In Switzerland these glacial meltwater are (1)_______ for hydropower. " the word required is used.

- the verb "used" is appropriate in this sentence to convey that the glacial meltwater is being used or harnessed for the purpose of generating hydropower.