男性精子中所含的性染色体是[ ]

A．XX染色体            

B．XY染色体  

C．X染色体或Y染色体    

D．YY染色体

The World Wide Web is sometimes jokingly called the World Wide Wait because it ________

be very slow.    [ ]

A. should          

B. must          

C. will              

D. can