— Is there a ______ as to when I should return the book? 

—  Yes. You have to put it back here no later than next Friday. [ ]

A. boundary

B. limit

C. length

D. degree

心房颤动时，心电图鉴别室性早搏与心室内差异传导，下列哪项最有帮助（）。

A.异常QRS波群前长间隙

B.以上都不是

C.起始向量

D.异常QRS波群呈右束支阻滞图形

E.室性融合波