33. Because of the current economic depression, days are gone when 5-star hotels in Shanghai ______ charge 6,0000 youn for one night.

A．had better

B．may as well

C．should

D．would rather

与乙炔具有相同的碳、氢百分含量，但一定既不是它的同系物又不是它的同分异构体的是  [ ]

A．丙炔   

B．乙烯     

C．C₄H₈  

D．苯