Which has the identical singular and plural form?

Advice' is a- Gallows এর plural কী? We shall not see his like again. Here 'like' is a/an - Plural of 'Man' is Which of the following word is singular? Which one is in the singular number? Which word is both a noun and a verb? Abstract noun of the word 'Long' is- The principal took the round in the college. Here 'Round' is a/an- The word 'American' is