以下符合代谢性酸中毒特点的是（）

A.HCO^-₃/H₂CO₃<20/1，原发性H₂CO^-₃↑

B.HCO^-₃/H₂CO₃<20/1，原发性HCO^-₃↓

C.HCO^-₃/H₂CO₃>20/1，原发性H₂CO₃↑

D.HCO^-₃/H₂CO₃>20/1，原发性HCO^-₃↓

E.pH值一定B降低

How this kind of plant can be ____ in a special way is still unknown to us.

A．kept away

B．kept out

C．kept alive

D．kept off