大学英语六级

oar oath obedience obedient objective obligation oblige obscure observation observe obstinate occurrence offence offensive offer offset offspring ohm olive opaque operation opium optical optimism optimum option orchard orchestra ordinarily orient orientation originate ornament ornamental otherwise ought outbreak outcome outermost outlaw outlet outline outside oval over overall overestimate overflow overhang overhear overlap overload overlook overseas overtake overthrow overwhelm overwhelming oxide oxidize oyster