Jim acted very strangely all day.
I think the correct spelling of the cloze word is συμπεριφερόταν or συμπεριφερότανε, which are third person singular. Συμπεριφέρονταν is third person plural. I have requested clarification from tatoeba.
Jim acted very strangely all day.
I have since looked up this verb in ‘Τα Ρήματα της Νέας Ελληνικής’ by Άννα Ιορδανίδου, and the ending as written is an option.
Jim acted very strangely all day.
Ι was a tad confused about that spelling, as well.
Strange, I have never seen or heard this form being used for the 3rd person singular.