Hi.
Im no expert but i have done this several times when sorting data from DOM.
I put all the result to list and then define a variable which is set to the first line you want to get, then you have to put that variable into the list parameter.
After you did that you do what you want with the line and at the end you use variable processing and add 3 to that variable. So if you where getting line 1 firstly, you will get line 4 next and line 7 after that.