"Throw the cake."
Yes, and just aim it at someone you reeeeeally dont like's face please...
I understand the 던지싶시오 even tho its a little weird to politely ask someone to do that. But if I were speaking in the informal polite tone (the one where you put 요 at the end) it's telling me that 던져요 is incorrect (even tho it's listed as one of the correct answers) and that 던지라 is the correct answer. What am I missing?
It actually is the imperative verb ending, for when you give orders. You are correct in the sense that it includes the "please" though, but that is because of the speech level this verb ending is in. In other words, this verb ending indicated formality and politeness, essentially "kindly asking" someone to do something (in comparison to say, barking orders at someone). The verb ending doesn't just mean "please" however (there isn't even direct translation of please in Korean!)