Which of the following word is regarded as 'singular'?

Singular is a grammar term that is defined as the form of a word used when discussing only one person, place or thing.There are some nouns like measles, mathematics, dominoes etc. that look plural but are singular. Thus, option 4 is the most appropriate choice.As English has constantly borrowed words from other languages throughout its history, there are many nouns with plural endings taken from the source language. For eg. Bacterium - Bacteria Datum - DataMedium -MediaThere are certain nouns that only have a plural form.For eg.- Police