class's — a number of persons or things regarded as forming a group by reason of common attributes, characteristics, qualities, or traits; kind; sort: a class of objects used in daily living.
classes — a number of persons or things regarded as forming a group by reason of common attributes, characteristics, qualities, or traits; kind; sort: a class of objects used in daily living.
gasses — Physics. a substance possessing perfect molecular mobility and the property of indefinite expansion, as opposed to a solid or liquid.