Hi, Cloe!
I agree with Andy. The web site you have cited models how to write down topic sentences very nicely and clearly. I like it when you have to make choices because it definitely guides you through the process and as a student I would really have a better understanding of what I am expected to produce for an academic paper.
I think another way to address topic sentences is by exemplifying this short pattern: Topic + controlling idea (comment, opinion on the issue). In Ecuador, my students and I used to work with it and many EFL textbooks provided examples, too . This link also models it that way.
http://www.eslbee.com/topic_sentences.htmI think what is interesting in the examples on this page is that the controlling idea leaves the reader with an expectation of what is coming next, which is another important characteristic of topic sentences. The quiz on the right allows you to identify the topic and supporting points for each example as well. What do you think of it? I hope you find it somewhat helpful, too.