Some nouns are used as singular forms even if they are in the plural form

Reading glasses over an open book

This category includes the nouns that are written in plural form, but they are used as singular forms.
In other words, you can see the plural suffix –s added at the end of the word, but the word itself is used as a singular in a sentence. So when you do the subject and verb agreement, it has to be in the singular form and not the plural form. The following words are a good example to understand this category:

Economics, Civics, Physics, Politics,

Athletics, Mathematics, Gymnastics.