How do you come up with these meaningless sentences?
"If I have learned anything, then this". Ok English is not my mother tongue but I doubt that this sentence makes sense anyway? These kind of sentences are a big source of frustration while using Duolingo. I really wonder if I should spend more time with it :-(
You're right. This sentence doesn't make sense in English. It reads as though the last part of the sentence has been left out. I think it's a glitch and should be reported.
Thank you for your answer. Yes, maybe a part of the sentence was stripped out or the sentence could make sense in the text it was taken from but this way, out of context, does not mean much. The bad thing with Duolingo is that you can find the same sentence 3 or 4 times during the same exercise and you are forced to use the bad sentence and its bad translation just to finish the exercise and go to the next one (I doubt this is very didactic).