To determine the leading run scorer in the calendar year 2008, we need to look at the performances of the players mentioned.
Option A) GC Smith - This option is incorrect because Graeme Smith, the South African cricketer, was not the leading run scorer in the calendar year 2008.
Option B) RT Ponting - This option is incorrect because Ricky Ponting, the Australian cricketer, was not the leading run scorer in the calendar year 2008.
Option C) G Gambhir - This option is incorrect because Gautam Gambhir, the Indian cricketer, was not the leading run scorer in the calendar year 2008.
Option D) KP Pietersen - This option is incorrect because Kevin Pietersen, the English cricketer, was not the leading run scorer in the calendar year 2008.
The correct answer is A) GC Smith. Graeme Smith, the South African cricketer, was the leading run scorer in the calendar year 2008.