Oh then it's easy.just select three expected column and then combine into one string and return as one column.then just bind the returning column as like as simple drop down list.
Sample Code:
List<ListItem> users = new List<ListItem>();
foreach (SubscriptionUser su in subscriptionDetails.UserList)
{
users.Add(new ListItem(su.FirstName + " " + su.LastName, su.EmailAddress));
}
ddlPrimaryContact.DataTextField = "Text";
ddlPrimaryContact.DataValueField = "Value";
ddlPrimaryContact.DataSource = users;
ddlPrimaryContact.DataBind();