Houses in China's big cities are so unreasonably expensive that generally young couples can't afford _______ without their parents' financial support.
A:that
B:it
C:any
D:one
某单细胞生物,没有叶绿体但有叶绿素,它最可能是 ( )
规定符号⊗的意义为:a⊗b=a+bab,那么﹣3⊗4等于( )