6. So little ______ about physics that the lecture was completely beyond me.
A. I knew
B.did I know
C.I had known
D. had I known

7._______ fairly recently _____solved, at least partially.
A. Until/ that this problem was
B.It was until /that this problem was
C.Not until/was this problem
D.It was not until/when thisproblem was

8.Only after he has acquired considerable facility in speaking _____to learn to read and write.
A. he began
B. will he begin
C.did he begin
D.must he begin

9.Busy ______ he is ,he can fulfill the task ahead of schedule.
A.because
B. as
C. no matter how
D.although

10.By no means ______ create or destroy energy.
A. we can
B.we can’t
C.can we
D.shall we

 B C B B C