Often there are multiple correct answers to a question, where if you are in a tapping, listening or word selection section of review, you can easily determine which direction/noun/verb is required. But if you are in a typing question/quiz one’s Difficult Words are going to blow up.
Some of this is due to courses not being “clean”, not specifying which is required, but other times there are just multiple correct answers.
For German, common multiple correct answer nouns/adjectives are …
das Menu (Menü) vs die Speisekarte
der Doktor vs der Arzt
dick vs fett
Wie Spät ist es? vs Wie viel Uhr ist es?
So one has to really remember which course one is, and often the course creator’s preference.
But, then there are verbs & verb combinations & separable verbs too!
3 verbs that cause considerable confusion are möchten, haben & müssen - largely due to a very large sliding scale regarding what “have” means in English. 4 months into learning German, I couldn’t tell you when gern, bitte or gern & bitte is required with möchten in a sentence… and it appears to revolve around how many levels of politeness one wants to cover in a phrase; none, 1, 2 or 3.
wollen - to want to and will (English) are also very difficult due to ich will, er/sie/es will having a much different meaning that i will, he/she/it will
werden & gehen/(ab)fahren + a specified time (heute Abend, etc.)
There are more examples… countless. This isn’t meant to be a complaint, but this morning alone with about 200 words to review, about 50 “words” entered my Difficult Words list… not only did they add over 30 minutes to my initial review period, but now they will take at least an hour to clear.
Phrase memorization is not truly learning how to use and be able interact with a language, but in many regards this is what the above pushes, more particularly in phrases/sentences learning in both Memrise & Duo.