Translation:I think I expressed myself very well.
Yes, the correct form is with the subjunctive (congiuntivo); dropping it for the indicative is very colloquial.
"I think I have expressed myself very well" should also be accepted as a valid translation of the sentence above.
If you are a woman, would you say "Mi sono espressa benissimo" (/benissima??) ??
Yes to "espressa". When essere is the auxiliary verb, the past participle changes with gender and with singular/plural (sono andato/sono andata, siamo andati/siamo andate). I think "benissimo" would stay the same because it's an adverb here, not an adjective, but I'm not 100% certain on that.
When a verb is reflexive (in this case the 'mi', meaning 'myself', makes it reflexive) it always uses the auxiliary verb 'essere' (here 'sono') instead of 'avere'.
I realise I'm an idiot, but I put "I think they expressed me very well" - for some reason I was imagining it was a painting they were talking about or something. It wasn't accepted obviously, but I'm not actually sure why not. Is it because it would revert back to 'hanno' when talking about others?
Yes :-) If "mi" were a direct object the verb would be used transitively, and all transitive verbs require avere.
Got it wrong because I didn't say "very". To whomever will comment "Benissimo" means very well, and Bene just means well. I understand, but it is unnecessary.
It is just as necessary as differenciating in English "well" from "very well"!...
In the earlier exercise I put Penso che mi sia espresso because I thought penso che always took the subjunctive. I'm not complaining because it was marked corect!
The last question did not have "che" in it, but the answer required "that" in it. Now this question HAS "che" in it, but the answer rejected "that" in it????????? Very confusing and annoying!!!!!!