Ads for financial trading apps /websites
The ads I see in the iPhone duolingo app (English, in Germany) are almost always for financial trading apps / websites. I'm posting this here in case the duolingo staff isn't aware and doesn't want these kind of ads (that appeal to the inner gambler in all of us).
There's nothing unwholesome about the stock market ... well, at least not in the same way that, say, roulette is unwholesome. The vast majority of Americans rely on the the stock market to fund their retirements. Invest in a smart way, and it's pretty much not gambling.*
*Assuming no unforeseeable global catastrophes such as a cretaceous size asteroid.