C). True. If you have a table named 123, which is not a standard naming convention because it begins with a digit, you can reference it in SQL by using double quotation marks. The correct syntax to reference a table with a name that does not follow standard naming conventions is to enclose the name in double quotation marks.
A, B, and D are incorrect because they do not use the proper quoting mechanism for a table named with non-standard characters. In Oracle, double quotation marks are used for case-sensitive table names or those that do not follow the usual naming rules.