Harrison Ford is thought to be one of the few movie stars ____ as a carpenter before.

A．to work

B．to be working

C．to have worked

D．to have been working

药物的pKa小于3

A．药物吸收得很慢
B．直肠液的pH值
C．栓剂距肛门约2em处
D．直肠内存有粪便
E．基质的熔点