David failed in the final examination last term and only then _____ how much time he had wasted before.[ ]

A. had he realized  

B. he had realized

C. did he realize  

D. he realized

有关一五计划的表述不正确的是

A．一五计划是在国民经济好转的基础上实施的

B．一五计划重点发展交通运输业

C．一五计划开始了我国艰难的工业化道路

D．一五计划的顺利完成，缩小了与发达国家的人均工业品拥有量的差距