Any reason why "This secret must REMAIN between us" should be incorrect?
Looks okay to me, they both have the same meaning in my opinion. Although I guess the one you gave is a little less common compared to duolingo's.
Agreed. No reason to be marked incorrect though. Thanks.
"Remain" is now accepted 8/7/15
How about "This secret must stay among us"?
Hum... for some reason that doesn't sound right to me.
Ok! I think, I understood! Thanks a lot, guys!
Why is "This secret needs to stay between us" NOT accepted?