Lessons beginning with test
Several of the lessons are starting out with requiring student translations on words that haven't yet been introduced. Is this just random luck? Or is this the way it is meant to be? I am having to totally guess, which is frustrating. When I guess wrong, I lose my "health" and I re-do the lessons.
Wait, there's no 'health' on DuoLingo anymore. But whatever. Words that haven't been introduced are yellow. If you're talking about 'Idioms' or 'Flirting' or whatever, yes, there will be new words that are not yellow. (You know, in the lessons you buy from the Lingot Store.)
All new words you see should be in an orange font. When you hover over these words you should see a pop up window with several translations of the word. The top option is usually the most applicable for the sentence in the test.
You can also hover over other words and get a translation but this weakens the strength of that word as it indicates you have not learned it yet.
I experienced a similar problem once while doing the Korean tree. In my case, the lesson started with Tap the pairs (on the app), so there were no written words to hover on and read. The result was that the exercise had too many unknowns to be done by ruling out the known words. The new words were then introduced individually in a following exercise.