Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Name | Background | Title | Appointment | Presentation of Credentials |
| --- | --- | --- | --- | --- |
| William H. Christensen | Non-career appointee | Chargé d'Affaires ad interim | August 31, 1962 | August 31, 1962 |
| Robert G. Miner | Foreign Service officer | Ambassador Extraordinary and Plenipotentiary | October 23, 1962 | December 1, 1962 |
| William A. Costello | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | September 13, 1967 | October 26, 1967 |
| J. Fife Symington, Jr. | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | July 8, 1969 | September 11, 1969 |
| Anthony D. Marshall | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | February 15, 1972 | February 22, 1972 |
| Lloyd I. Miller | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | December 19, 1973 | February 8, 1974 |
| Albert B. Fay | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | February 4, 1976 | February 17, 1976 |
| Richard K. Fox, Jr. | Foreign Service officer | Ambassador Extraordinary and Plenipotentiary | July 8, 1977 | July 21, 1977 |
| Irving G. Cheslaw | Foreign Service officer | Ambassador Extraordinary and Plenipotentiary | September 28, 1979 | October 18, 1979 |
| Melvin Herbert Evans | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | December 1, 1981 | January 1, 1982 |
| Sheldon J. Krys | Foreign Service officer | Ambassador Extraordinary and Plenipotentiary | July 12, 1985 | August 19, 1985 |
| Charles A. Gargano | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | July 15, 1988 | August 9, 1988 |
| Sally G. Cowal | Foreign Service officer | Ambassador Extraordinary and Plenipotentiary | August 2, 1991 | August 27, 1991 |
| Brian J. Donnelly | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | July 5, 1994 | September 5, 1994 |
| Edward E. Shumaker III | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | October 24, 1997 | January 13, 1998 |
| Roy L. Austin | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | October 1, 2001 | December 6, 2001 |
| Beatrice Wilkinson Welters | Non-career appointee | Ambassador Extraordinary and Plenipotentiary | April 27, 2010 | 2010 |
| Margaret B. Diop | Foreign Service officer | Chargé d'Affaires ad interim | October 2012 | Unknown |
Question:
Who presented their credentials at an unknown date?
Answer:
Margaret B. Diop