—How many English parties ____ by the end of last term?        

—Sorry, I can't remember. [ ]

A. did you have    

B. had you had    

C. have you had

已知同种元素的含氧酸中，成酸元素的化合价越高，其含氧酸的酸性越强。下列无机含氧酸中酸性最强的是 [ ]

A.HNO₂

B.H₂SO₃

C.HClO₃

D.HClO₄