There are three groups of nouns that we use only in the plural. We use them with plural verbs and plural pronouns:
Your glasses are dirty. Take a tissue to wipe them.
These groups of nouns are:
1) Nouns related to items consisting of two parts (glasses, scissors, jeans, trousers…)
My new trousers are so cosy.
You can talk about them in singular if you use ‘a pair of’:
This pair of scissors is very sharp.
2) Nouns ending in –S (clothes, stairs, belongings, thanks, congratulations…)
These clothes are dirty.
The stairs in their house were too narrow.
Remember that these nouns are countable as they answer the question how many, not how much.
How many belongings have you got?
3) Nouns which express groups of people or animals (police, cattle, folk, people, poultry…)
The police are in front of the building.
They use growth hormones to make cattle grow faster.