"They are different."
I do not think so, 「彼らは変わっています」 means either "They are strange" or "They are changing", but not "They are different".
I see. However we often say " <they are> different " to mean " they are strange" and also to mean " they are distinct from others" depending on context.
Thank you for your suggestion. I immediately looked it up in a dictionary and found "strange" was one of translations of "different", but with a comment "it is colloquial (e.g. http://ejje.weblio.jp/content/different). This may be a reason why 「変わっている」 is not included in the correct answers (to avoid learners' confusion).
Anyway, I learned a lot through this communication and would like to thank you.
Not at all, I'm happy to help, and I understand the need to limit scope sometimes. A similar phrase is " <he is> funny " with the meaning of 'strange / 変わっている'
I learnt something too :-)