CFA Mock I morning Eco re Daltonia

Q. 6. I worked out the European investor can make €1.8k from just borrowing in Eur and investing in $ (and not DRN) which is higher return than €1,065 where the invetors borrows in Eur, converts to USD and then to DRN and back to EUR. Why is the above answer not included? or should i assume that one has to use all the currencies involved?