How many more decades will have to pass （）　scientists succeed in providing a cure for cancer？

A．kills large numbers of Eastern peoples
B．is a vitamin deficiency （缺乏） disease
C．is caused by diseased deer
D．can be caught from diseased chickens

A．have much difficulty understanding each other
B．lack confidence
C．dare not cope with any problems alone
D．are very much afraid of getting lost

A．human activities could not continue
B．there could not be weather forecasting systems
C．many activities would have to change their present form
D．banks would not be able to go on with check clearing