I'm having brain death when it comes to the following concepts:
1. alguno alguna algunos algunas - when to use the singular forms vs. the plural forms
2. ninguno ninguna ningunos ningunas - when to use the singular forms vs. the plural forms
3. I cannot distinguish between pero and sino que. i Have no problem with sino, itself.
I have read the explanations of these topics at least 10 times and I still get them wrong in my quizzes. During my reading of the explanations my brain gets all fogged up and I can't make the necessary distinctions.