— I'm sorry I didn't make it to your party last night.  

—  ____. I know you are busy these days.   [ ]

A. Of course.      

B. No kidding.  

C. That's all right.    

D. Don't mention it.

传播途径是指（）。

A.病原体更换宿主的过程

B.病原体自传染源排出的过程

C.病原体更换宿主在外界环境下所经历的途径

D.病原体侵入易感者的过程