6.70 How to make different Grids

Grid[{ 
  {Item[a, Alignment -> Center], b}, 
  {SpanFromAbove, c}}, Frame -> All] 
 
Grid[{ 
  {Item[a, Alignment -> Center], Item[Column[{b, c}]]}}, Frame -> All] 
 
Grid[{ 
  {Item[a, Alignment -> Center], Item[Column[{b, c}, Frame -> All]]}}, Frame -> All] 
 
Grid[{ 
  {a, Item[b, Alignment -> Center]}, 
  {c, SpanFromAbove}}, Frame -> All] 
 
Grid[{ 
  {Item[a, Alignment -> Center], Item[b, Alignment -> Center], c}, 
  {SpanFromAbove, SpanFromAbove, d}, 
  {SpanFromAbove, e, f}}, Frame -> All]