Which plural word can be used as singular?

Which plural word can be used as singular? Correct Answer ethics

The plural word that can be used as a singular is "ethics" While "ethics" is typically a plural noun, it can also be used as a singular noun when referring to the study of ethics or a particular system of ethics. For example, "Ethics is an important subject to study" or "Utilitarian ethics is a popular ethical framework."The other words, "books," "princes," and "universities" are generally not used as singular nouns. However, in certain contexts, "book" can refer to a single volume or edition of a book, "prince" can refer to a single male member of a royal family, and "university" can refer to a single institution of higher education.