According to the rules of the factory, you can ask for leave ________ you have a doctor's diagnosed

note.[ ]

A. now that        

B. on condition that      

C. unless    

D. even though

以医院为基础的病例对照研究，最常见的偏倚是

A．观察偏倚

B．信息偏倚

C．混杂偏倚

D．选择偏倚

E．错分偏倚