A:think , are
B:am thinking,are
C:thought, were
D:think, were
甲、乙、丙三个物体,甲静止地放在北京,乙静止地放在江苏,丙静止地放在广州.当它们随地球一起转动时,则( )
人、噬菌体、禽流感病毒中参与构成核酸的碱基种类数分别是( )
下列关于生物圈的说法正确的是( )