How to use 'Most of the + nouns'

‘Most of the + nouns’ can be followed by singular verbs or plural ones, depending on which nouns are used.

a) If the nouns are countable, the plural verbs are used.

e.g. Most of the books sold in the bookshop are cheap.

Most of the boys learn how to spell well.

b) If the nouns are uncountable, then singular verbs are used.

e.g. Most of the water in the area tastes salty.

Most of the petrol sold in this country is imported.