i have web page that save data for stores, these stores have activities i want to determine the activities for those stores. this reason i make three tables: first one is :

tbOLActivity has fields: ActivityId int (pk), ActivityName nvarchar(50)

second one is :

tbOLStore has fields: StoreId int (pk), StoreName nvarchar(50), ActivityId int (fk), Address navrchar(50)

therd one is:

tbOLStoreActivty has fields : SerialNo int (pk), StoreId int (fk), ActivityId int (fk), Activity_Status int

i make combobox in web page called "AcivityCombo" to display the data of tbOLActivity table

 If CtvAct.GetRecords("Fill_ActivityTb") = True Then
                AcivityCombo.DataSource = CtvAct.MainDataset.Tables("tbOLActivity").DefaultView
                AcivityCombo.DataTextField = "ActivityName"
                AcivityCombo.DataValueField = "ActivityId"
                AcivityCombo.DataBind()

the problem is how to select item from this combo and insert it into gridview then save data into the tables