how to style concatinated string in code behind

I have some search criteria like drop down and below i have a dive in which i have a label control i am binding this label control to selected values of dropdown which  are  used as parameters above now i want to bold just the dropdown selected value i do not want the drop down values to be style i just want this label string is style like below 

lblSummary.Text = "This is the report of District " & ddlDistrict.SelectedItem.Text.ToString() & 

 

I want this drop down value to be bold when concatinating with lblsummary.text