Hello. I'm happy you find it useful.
I do not take the course, so I'm not sure abt quiz. In everyday life, honestly it is quite weird to say "I can say thank you."
To exaggerate about a foreign language, imagine meeting an alien from outer space. If he/she/it can say "thank you" (in English), you will be quite impressed already! Saying in a full phrase conjures the image that you are bragging. Since you can form a phrase already, there's nothing shocking about the fact you can say "thank you." (To me it seems so, at least.)
Another phrase most beginners learn for any language is to speak "I don't know X language" in that language itself. For example, wo bu dong zhong wen. I don't know Chinese. (But contradictorily, you are speaking Chinese) That's another weird phrase people learn. If others can't tell you really can't understand except a few phrases, you might be dismissed as a rude guy.
I read what I've typed above and that's not quite satisfactory. So here's take 2. A quick online dictionaries searches and translations,
Able to do smt
HUI (Shows possibility) My little brother can walk now.
Should. You shouldn't talk of him this way.
Scientific: NENG LIANG energy
可能、能够，也表示允许 你可以吃了。 Nĭ kĕyĭ chī le.
Shows possibility, Able to do smt, Permitted to do smt.
Example: You can eat now.
理解、懂得 他会汉语。 Tā huì hànyŭ.
Understand, know (smt). He knows HAN YU (Chinese).
4. verb understand; grasp
5. verb be good at; be skillful in
6. verb can; be able to
7. verb be likely to; be sure to; will; would
There you go.
Funnily, anyone know the difference between Han Yu, hua Yu, hua wen and zhong wen? Haha I'm confused. I used them interchangeably because I can't differentiate them. Haha