check from which checkedlistbox items are

I have two checkedListBoxes(checkedListBox1 and checkedListBox2) and one listBox1, where are items from both checkedListBoxes. I want to perform a check something like this:

 if listBox1.CheckedItem is from checkedListBox1 do...
    else if listBox1.CheckedItem is from checkedListBox2 do....

I have one button for passing items TO listBox and second one for passing values FROM listBox and i have trouble performing check from which checkedListBox items are.

I passed items to listBox like this:

string[] stringArray = new string[checkedListBox1.CheckedItems.Count];
listBox1.Items.AddRange(stringArray);

Of course with some checkings and cycles and same for other string[].