对于脐带，下列哪项是不恰当的（）

A.妊娠足月（40周末），脐带一般长度为50cm

B.脐带表面有羊膜包围

C.脐带含有一条脐静脉和两条脐动脉

D.脐带杂音的速率与胎心率相同

E.脐静脉的氧分压低于脐动脉

Last week, only two people came to look at the house,          wanted to buy it.   [      ]

A. none of them      

B. both of them      

C. none of whom    

D. neither of whom