Why do they become
as in lopen - loop
What are the rules behind them?
Datum: 12:31 25-02-2016
Hi, you asked the question quite a while ago already just in case you didn't have the answer yet.
If you make lopen singular by removing the -en you get the word lop. As lop which sound different from lopen. So to keep the same pronunciation this verb is irregular and you have to add an -o (loop). The other verbs are regular ;)