How to validate a drop down list for a web form on Microsoft Visual Studio?

Link to rubric and code. This is for chapter 9 as I am trying to provide as much details as possible:

https://1drv.ms/u/s!AnJ4ilz1MKZlga4rg7cPsTPereF_8g?e=3acLyL

' Hi, I'm trying to create a web form using Microsoft Visual Studio. Under the comment, "Ensure a Taco Selection is Selected," what is the proper code to validate that a drop-down list has been selected? I have not yet begun validating that a check box has been selected. Would they use the same method of code? If not, how can I validate that a check box has been selected?

' I have tried to use the standard If-Then or If-Else statements but I keep receiving error messages.

' I apologize for mixing my question with the code, as I am not sure how to keep them separate

' Project: Street Tacos Order Form ' Author: Richard Lew ' Date: November 3, 2019 ' Purpose: The web application allows a customer to fill out a street taco order form.

Public Class About Inherits Page

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load

End Sub

Protected Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
    ' The btnSubmit click event will calculate the cost of the street tacos
    ' based on the type of tacos selected.

    ' Declare and initialize variables
    Dim decChickenCost As Decimal = 8.99D
    Dim decPorkCost As Decimal = 9.99D
    Dim decFishCost As Decimal = 12.99D
    Dim decBeefCost As Decimal = 13.99D
    Dim decExtraCost As Decimal = 0.99
    Dim strName As String
    Dim strAddress As String
    Dim strPhone As String
    Dim decOrderCost As Decimal = 0D
    Dim strMessage As String

    ' Trim additional spaces that are entered by the user
    strName = txtName.Text.Trim
    strAddress = txtAddress.Text.Trim
    strPhone = txtPhone.Text.Trim

    ' Clear the Order Message
    lblOrder.Text = ""

    ' Ensure a Taco Selection is Selected
    If (ddlTacoType.SelectedIndex == 0) Then
        {            {
        lblTacoTypeError.Visible = True
        }
    End If
End Sub

End Class

' The code should prompt the user to select a taco from the drop-down menu and to select at least one check box.