A:who is it
B:who it i
C:it is who
D: it is whom
动物细胞中的能量转换器是( )
_______ he is tired, he is still doing his homework.
体积是5分米3的铁球重39.2牛,将它放人水中,它将 ( )
战国时期,主张“兼爱”、“非攻”的是( )