Instead to giving the value to choice it is giving the value Microsoft.Xrm.Sdk.OptionSetValue

i am writing the code 

Entity entity = context.InputParameters["Target"] as Entity; string caseTitle = string.Empty; //initialize
string dateTime = string.Empty; string priority = string.Empty; string DD = string.Empty; caseTitle = entity["cr117_subject"].ToString(); dateTime = entity["new_createddate"].ToString();
priority = entity["new_priority"].ToString();
DD = caseTitle +"|"+ dateTime+"|"+ priority; entity["cr117_subject"] = DD;