--So can I ask you a few personal questions?

---No problem. I like ________ when people are open and direct.

A．that

B．this

C．it

D．them

有高碳酸血症的慢性呼吸衰竭者，最适宜的浓度是

A．15%～20%
B．25%～30%
C．35%～40%
D．40%～50%
E．75%～80%