(You can learn about the difference between countable and uncountable nouns here.)
Practice 1: uncountable or plural noun?
Choose the best word to complete these sentences: is the noun uncountable (no -s) or should it be a plural, countable noun (-s).
Practice 2: a or some?
Now try this exercise: choose 'a' if the noun is singular, and 'some' if it is uncountable.
Practice 3: countable or uncountable?
Some nouns (for example the ones below) can be countable or uncountable, depending on the situation. Choose 'a' if you think it's countable, or '-' if you think it's uncountable.