Verb conjugation of "differentiate" in English

It looks like we need to invite Erika again to my home, once the cake is ready. Of course, this should be done before Sunday to stay in the chocolate cake race. We should buy cream too.
Anyway, there are a lot of people on board and I no matter how high the waves may be, I always suffer from nausea or seasickness. I have not been on a small boat before. I will have to vomit.
This is a fantastic idea, I am learning German just since last year. I speak, write and read well, and I will improve soon. This site, Vocabulix, I'm visiting often and I am mostly online.