it CAn BE inFErrED thAt DinosAurs' low-oxygEn ADAptAtion _________.
A．wAs uniquE in Evolution
B．EvolvED out oF thE low-oxygEn EnvironmEnt hunDrEDs oF million yEArs Ago
C．is hArD to ExplAin
D．CAusED thEir ExtinCtion