Translation:This movie is scary.
more correctly the measure word 部 should be used, though realise it's not essential. Just saying....
true, but Duolingo is particular about other measure words like 条 and 件. So, I think it should be consistent that the correct measure word be used.
This thing is getting more and more prescriptive for AMERICAN English and is more and more rejecting any other kind of English especially English English! )-:
Usually they want "tai4" for 'too (much)', "hen3" stands for "very" or is just used as a link and is not translated at all
To split hairs, you could say 这是一个可怕的电影 (zhe shi yi ge ke pa de dian ying)。But for me they're both pretty much the same.
I guess in English the difference may be that a scary movie may be more like a category and the movie is scary is saying more about your opinion. Don't know if it is similar in Chinese.