Grupo de consulta de Linq al seleccionar los primeros elementos

Tengo una matriz String algo así:

// icon, category, tool String[,] subButtonData = new String[,] { {"graphics/gui/brushsizeplus_icon", "Draw", "DrawBrushPlus"}, {"graphics/gui/brushsizeminus_icon", "Draw", "DrawBrushMinus"}, {"graphics/gui/freedraw_icon", "Draw", "DrawFree"}, {"graphics/gui/linedraw_icon", "Draw", "DrawLine"}, {"graphics/gui/rectangledraw_icon", "Draw", "DrawRectangle"}, {"graphics/gui/ellipsedraw_icon", "Draw", "DrawEllipse"}, {"graphics/gui/brushsizeplus_icon", "Brusher", "BrusherBrushPlus"}, {"graphics/gui/brushsizeminus_icon", "Brusher", "BrusherBrushMinus"}, {"graphics/gui/brushsizeplus_icon", "Text", "TextBrushPlus"}, {"graphics/gui/brushsizeminus_icon", "Text", "TextBrushMinus"}, }; 

Luego mainButtons un List