CellBracketOptions -> {opt_1 -> val_1, opt_2 -> val_2, ...} is an option for cells that specifies settings for cell brackets.
C
(Built-in Mathematica Symbol) C[i] is the default form for the i\[Null]\[Null]^th parameter or constant generated in representing the results of various symbolic computations.
CommonDefaultFormatTypes -> {opt_1 -> val_1, opt_2 -> val_2, ...} is an option that specifies default formats for newly created cells.
DefaultFormatType is an option for cells that specifies the format used for displaying expressions in a newly created cell.
DefaultInlineFormatType is an option for cells that specifies the format used for displaying expressions in a newly created inline cell.
DiacriticalPositioning is an option for UnderscriptBox and related boxes that specifies how close diacritical characters are drawn to the base character.
ImageRegion is an option for cells that specifies the size and position of the bounding box within which a graphic is rendered.
Language is a global option that specifies the language in which menus, dialog boxes, error messages, and help files are displayed.
MultilaunchWarning is a global option that specifies whether a warning is given when you try to modify user preferences while running two copies of Mathematica simultaneously.
MultilineFunction is an option for UnderscriptBox and related box objects that specifies what to do when the contents of a box object are too long to fit on one line.