血氧饱和度主要取决于（）

A.血O₂含量

B.PCO₂

C.Hb水平

D.PO₂

E.血pH

- Oh,  these presents are so nice.

-  The CD is from Betty and the books are from________.[ ]

A.  I and Helen        

B.   Helen and me

C.   Helen's and mine    

D.   Helen and I