Monogame in vs2010 running problem

hi,
A new monogame project after the operation on this error, what should I do, please give advice or comments

Error 1 type “Android. App. The Activity” in the definition not referenced assemblies. Must be added to the assembly “Mono. Android Version = 0.0.0.0, Culture = neutral, PublicKeyToken = 84 e04ff9cfb79065” reference. D: \ xm \ GameName1 \ GameName1 \ Activity1 cs 16 GameName1 18