For the purification of alumina,the modern processes most useful when $(i)$ the impurity present is a lot of iron oxides and $(ii)$ the impurity present is a lot of silica,are:

• A
  For $(i)$ Hall's process; for $(ii)$ Baeyer's process
• B
  For $(i)$ Hall's process; for $(ii)$ Serpeck's process
• C
  For $(i)$ Serpeck's process; for $(ii)$ Baeyer's process
• D
  For $(i)$ Baeyer's process; for $(ii)$ Serpeck's process