is "per" not "for"? It would make the same sense in English to say "which is the street for the museum" so I dont understand why it is incorrect.
Agreed: "Which is the street for the museum" is perfect English. I have reported it 14.7.14
April 2019, It accepts "What is the street for the museum" - so it doesn't like "which..."
Well I was given "street" as the answer! It seems to depend on the other words you choose - i.e. if you use "street" it must be "the street that goes to the museum". The word route is an alternative to "the street that goes to", I suppose.
quale/qual is which that is which one of the available options. Since there are many options to choose to go somewhere, use qual to ask which one of them leads to the museum.