Having been out of touch with his parents for two years, John returned home,           

A．safe and sound

B．safely and sound

C．safe and soundly

D．safely and soundly

在一个正常女性的体细胞中含有 [ ]

A．两个X染色体  

B．一个X染色体一个Y染色体

C．两个Y染色体

D．一个X染色体