How to disable the item for GtkComboBox?

["Tom Liu" <tom liu flextrade com>]

Hi
According the Gtk documents. Looks like GtkComboBox will replace the
GtkOptionMenu. GtkOptionMenu is deprecated.

1: Can I disable some item of GtkComboBox?
2: How can I set the font and color for the GtkComboBox dropdown menu?

The GtkOptionMenu has a function gtk_option_menu_get_menu allow me to
access the menu. What's the similary function for GtkComboBox?

Thanks.