I hear the children have problems ______ the zoo. [ ]

A to get to          

B to getting        

C getting to          

D getting at

确诊CO中毒最主要的依据是

A．空气中CO的浓度

B．与CO接触的时间

C．血液中碳氧血红蛋白的有无

D．昏迷的深度

E．缺氧的程度