— Putting on a happy face not only helps us make friends but also makes us feel better.    

— _____.  [      ]

A. I'd love to                  

B. I'm with you on that      

C. It's up to you                

D. It's my pleasure

注射疫苗的目的是 [ ]

A．控制传染源

B．切断传播途径

C．保护易感人群

D．治疗疾病