From to the combobox you have a Member value and Display value when you are add some item to the combobox but you can`t use them with
so you can use
but don`t forget before than use it you should initial DisplayValue and MemberValue properties.
strsql = "select id,Title from Table1 "
ComboBox1.DisplayMember = "Title"
ComboBox1.ValueMember = "id"
ComboBox1.DataSource = MyDataSource
and you can fill your data source (MyDataSource) with SqlDataAdapter object with fetching data by your query. finally when you want to the bind second ComboBox you should use SelectedValue properties of fist ComboBox for example:
strsql = "select * from groupe where Activity_Name=' " & ComboBox1.SelectedValue& " '"
Of course if you want use ComboBox.Text you can use it but, you should change something to the from of your database.