Asp.net GridView启用行选择

我正在asp中使用GridView。网我想选择一个数据行。我在属性面板中查找了MultiSelect和SelectionMode，但找不到。

那么，如何在GridView中启用选择行呢？

谢谢

代码隐藏

public partial class SearchCourse : System.Web.UI.Page
{
Connection dbCon;
DataTable tbl;

protected void Page_Load(object sender, EventArgs e)
{
    dbCon = new Connection();


}
protected void RadioButton1_CheckedChanged(object sender, EventArgs e)
{
    if (RadioButton1.Checked) {
        txtSubName.Enabled = true;
        comboSemester.Enabled = false;
        comboYear.Enabled = false;
        comboProgram.Enabled =false;
        txtSubName.Text = "";
    }
}
protected void RadioButton2_CheckedChanged(object sender, EventArgs e)
{
    if (RadioButton2.Checked) {

        comboProgram.Enabled = true;

        if (comboProgram.SelectedItem.ToString() == "Foundation Course")
        {
            comboSemester.Enabled = false;
            comboYear.Enabled = false;
        }
        else {
            comboSemester.Enabled = true;
            comboYear.Enabled = true;
        }
        txtSubName.Text = "";
        txtSubName.Enabled = false;
    }
}

protected void imgBtnSearch_Click(object sender, ImageClickEventArgs e)
{
    if (RadioButton1.Checked) {
        String name = txtSubName.Text;
        tbl = dbCon.getResultsBySubjectName(name);
        GridView1.DataSource = tbl;
        GridView1.DataBind();
    }
    else if (RadioButton2.Checked)
    {
        String program = comboProgram.SelectedItem.ToString();
        String year = comboYear.SelectedItem.ToString();
        String sem= comboSemester.SelectedItem.ToString();
        tbl = dbCon.getResultsByProgram(program,year,sem);
        GridView1.DataSource = tbl;
        GridView1.DataBind();
    }
    else if (RadioButton3.Checked)
        {
            String name = txtSubName.Text;
            tbl = dbCon.getResultsBySubjectNo(name);
            GridView1.DataSource = tbl;
            GridView1.DataBind();
        }

}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    String program = comboProgram.SelectedItem.ToString();
    String year, sem;
    if (program == "Foundation Course")
    {
        comboYear.Enabled = false;
        comboSemester.Enabled = false;
        year = null;
        sem = null;
    }
    else {
        comboYear.Enabled = true;
        comboSemester.Enabled = true;
        year = comboYear.SelectedItem.ToString();
        sem = comboSemester.SelectedItem.ToString();
    }

    tbl = dbCon.getResultsByProgram(program, year, sem);
    GridView1.DataSource = tbl;
    GridView1.DataBind();
}

protected void comboYear_SelectedIndexChanged(object sender, EventArgs e)
{
    String program = comboProgram.SelectedItem.ToString();
    String year = comboYear.SelectedItem.ToString();
    String sem = comboSemester.SelectedItem.ToString();
    tbl = dbCon.getResultsByProgram(program, year, sem);
    GridView1.DataSource = tbl;
    GridView1.DataBind();
}
protected void comboSemester_SelectedIndexChanged(object sender, EventArgs e)
{
    String program = comboProgram.SelectedItem.ToString();
    String year = comboYear.SelectedItem.ToString();
    String sem = comboSemester.SelectedItem.ToString();
    tbl = dbCon.getResultsByProgram(program, year, sem);
    GridView1.DataSource = tbl;
    GridView1.DataBind();

}



protected void RadioButton3_CheckedChanged(object sender, EventArgs e)
{
    if (RadioButton3.Checked)
    {
        txtSubName.Enabled = true;
        comboSemester.Enabled = false;
        comboYear.Enabled = false;
        comboProgram.Enabled = false;
        txtSubName.Text = "";
    }
}
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{

}

}

GridView代码