En esta oración, por es una preposición que expresa causa o motivo y qué es un pronombre interrogativo 1 que representa aquello que se ignora. Aug 23, 2008i find "no" can either be followed by a plural noun or by a singular noun if the noun is a countable one, but i don't know if the two phrases can be used interchangeably to a great degree or. May 21, 2019"if no" can be used for yes/no questions on forms and in questionnaires, yes.