单项选择题
A．was the first reliable experiment in language study in history B．proved what it meant to prove C．was not necessarily sound though based on observation D．was utterly ridiculous and not worth mentioning
A．they are innocuous agencies B．they are the causative agents of most human cancer C．they seem to be infections to many people D．they are generally thought to be relevant to most cancer in man
A．a film or concert occurs every Wednesday at 7 p. m. B．the full list would be too long C．films and concerts cannot be announced publicly D．the full list is not ready yet