Andrew Su, CEO at brokerage Compass Global Markets said the average cost of producing gold in Australia, home to some of the world's biggest gold miners, has jumped from $500 an ounce in 2007 to over $1,000 an ounce this year.
Persons (plural) is a very formal word. We only use it in rather legalistic contexts: [notice in a lift] Any person or persons found in possession of illegal substances will be prosecuted.
No, the word 'themselves' is a reflexive or intensive pronoun, in the third person, plural. The reflexive/intensive pronouns are: myself, yourself, himself, herself, itself, ourselves, yourselves, themselves. The children will pick up their rooms themselves. The children themselves cleaned their rooms.