Leonardo da Vinci(1452-1519)__________ birds kept in cages in order to have the pleasure of setting them free.

A．is said to be buying

B．is said to have bought

C．had said to buy

D．has said to have bought

pKa（）。

A.是解离常数的对数，其值等于药物解离50%时溶液的pH值

B.是解离常数的负对数，其值等于药物解离50%时溶液的pH值

C.是解离常数的对数，其值等于药物解离95%时溶液的pH值

D.是解离常数的负对数，其值等于药物解离95%时溶液的pH值

E.是解离常数的负对数，其值等于药物解离100%时溶液的pH值