I suppose in English we're supposed to assume moose is singular, not plural.
You can tell it's singular because it says "the moose eats" instead of "the moose eat". :)
They marked "The mouse eats the apple"as wrong, preferring "eating" instead. Seems like they should have accepted it. Gonna report.
Amd now I jist eent back to the exercise and saw that my keyboard "corrected" moose and turn dnitninto "mouse" there too. Oh well...