Translation:Please consult a dictionary.
If "a" or "the" isn't accepted, please do report it. But I don't think this is so much a problem with the course as it is a difference between English and Japanese. When I teach English in Japan, I tell the students, "open your textbooks", and then the Japanese teacher will say 「きょうかしょひらいて」. The teacher doesn't say あなたたちのきょうかしょ, because that's not typically how they speak. So the translation doesn't have to be "your", but it has the potential to be.
No, not usually. But what if you were one centimeter tall, standing next to a dictionary which towers over you, and your friend notices a spider on the cover?
OR what if in your group of friends there's one guy you all call "The Dictionary" because he knows a lot of obscure facts, and one night you realize none of you have his phone number?
But of course neither of those scenarios are what's happening here.