— You ought to have learnt all these sentences by heart.  

— ____, but I forgot everything when I was asked to recite them in front of so many students.   [ ]

A. So I ought to

B. So I did

C. So must I

D. So did I

力士乐A11VLO-LRDU1型泵的比例电磁铁线圈的工作电压为（）。

A.17V

B.13V

C.12V

D.15V