WASHINGTON - US Secretary of State Hillary Clinton has chosen Marc Grossman, a retired diplomat and former ambassador to Turkey, as the Obama administrations new Special Representative for Afghanistan and Pakistan, a senior State Department official has revealed. Grossman, who left the State Department in 2005 and is presently the vice chairman of a consulting firm, will succeed Richard Holbrooke, who died of a torn aorta in December 2010, The New York Times reported Tuesday. Mrs. Clinton met with Grossman on Monday, and he was introduced to the members of late Holbrookes staff, the official said on the condition of anonymity, as the appointment is yet to be officially announced.