how to change xaml content dynamically using c# with dynamic attrubutes?

i have a code:

Xaml:

<TextBlock x:Name="MondayTest"  /><TextBlock x:Name="TuesdayTest" />               

c#

string todayDay = System.DateTime.Today.DayOfWeek.ToString();

switch (todayDay){                      
case "Sunday":                                             case "Monday":
 //any idea to put string   today+Test.Text="today is "+ today?
// here the textblock sundayTest must be selected //if todayDay is sunday ,textblock mondayTest must be //selected if   todayDay is monday              
break;            
default:
//default value
break;
}