'He' 'him' 'his' are the correct pronouns in the case of not knowing the sex of the person being referenced.
Use of 'they' 'them' 'their' is plainly incorrect, and use of 'she' and 'her' is a modern social justice graffiti on the English language. The pronouns starting with x and z indicate untreated mental disorder in the user.
Use of 'they' 'them' 'their' is plainly incorrect, and use of 'she' and 'her' is a modern social justice graffiti on the English language. The pronouns starting with x and z indicate untreated mental disorder in the user.