A composite disc is to be made using equal masses of aluminium and iron so that it has as high a moment of inertia as possible. This is possible when

• A. the surfaces of the disc are made of iron with aluminium inside
• B. the whole of aluminium is kept in the core and the iron at the outer rim of the disc
• C. the whole of the iron is kept in the core and the aluminium at the outer rim of the disc
• D. the whole disc is made with thin alternate sheets of iron and aluminium