---If you       to my birthday party last Saturday, you would have met Jim.

---I was not in Beijing then, otherwise I       to your party.

A．came; would have come

B．had come; would have come

C．would have come; had come

D．would come; had come

我国政府为在20世纪末在我国消灭小儿脊髓灰质炎，近几年来，在每年的12月和次年的1月，对全国6周岁以下的儿童进行强化免疫，服用脊髓灰质炎疫苗．从预防传染病流行的角度看，这样做的目的是为了：（　　）

A．人工免疫

B．控制传染源

C．切断传播途径

D．保护易感人群