sentences:  When the antecedent is a specific group of two or more people, the pronoun "they" is used, again without any difficulty arising.And when the antecedent is generic and plural, again the pronoun "they" is used and is not problematic, because "they" is not gender-specific.But difficulty arises in choosing a singular pronoun to refer to a single, unspecified human (whose gender is indeterminate, as the reference is equally to a hypothetical male or a hypothetical female).