If you want to become a doctor, you ought to study( )

A. late 1960s

B. the late of 1960s

C. late of 1960s

D. late of the 1960s

A. in dark

B. in the dark

C. in a darkness

D. in darkness

A.in order that　　B.so that　　C.in order to　　 D.so as not to