Meee ..
For the barometer tube , First i chose B .. then rubbed it and chose C : (
For the echo , i chosed XW(im not sure about the letters) .. but its the shortest wall under the source of sound
For the Fuse .. The circiut breaker in the live wire ( at X ) .. and the fuse at y ..
For the cooper .. me too .. i chosed the other end of the wood
indeed , it was tricky