"Is that cheap?"
I know this question is a year old... but I'm still a tad confused. I thought one of the big details of Japanese was subject ambiguity... which I would think would allow "That" (Are wa) to be omitted and assumed--given the speaker is talking to someone that is holding the subject. At least that's the context in which I pictured this. Any other explanations is greatly appreciated.
Yes that is correct, but then I suppose in this scenario the person talked to is not holding the subject.
Theres really not such a thing as subject ambiguity in actual conversation, the subject might be technically ambiguous, but it should always be clear what is meant from the context.
In this case, Note that "are wa" is used, not "sore wa". Sore means "That", Are means "That (over there, away from both speaker and listener) indicating that the speaker is not refering to something the other person is holding, in which case ommiting the subject would be too ambiguous.
Either way, its hard to infer what kind of behaviour is needed regarding leaving the subject from the sentence in Duolingo, a single sentence is just not enough context.