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:
| Outcome | Date | Championship | Surface | Opponent in the final | Score in the final |
| --- | --- | --- | --- | --- | --- |
| Runner-up | 2 November 1992 | Guarujá, Brazil | Hard | Carsten Arriens | 6–7, 3–6 |
| Runner-up | 3 October 1994 | Palermo, Italy | Clay | Alberto Berasategui | 6–2, 6–7 (6–8) , 4–6 |
| Winner | 14 November 1994 | Buenos Aires, Argentina | Clay | Javier Frana | 6–3, 5–7, 7–6 (7–5) |
| Runner-up | 13 May 1996 | Hamburg, Germany | Clay | Roberto Carretero | 6–2, 4–6, 4–6, 4–6 |
| Runner-up | 29 July 1996 | Kitzbühel, Austria | Clay | Alberto Berasategui | 2–6, 4–6, 4–6 |
| Runner-up | 7 October 1996 | Marbella, Spain | Clay | Marc-Kevin Goellner | 6–7 (4–7) , 6–7 (2–7) |
| Winner | 14 April 1997 | Estoril, Portugal | Clay | Francisco Clavet | 6–3, 7–5 |
| Runner-up | 28 April 1997 | Monte Carlo, Monaco | Clay | Marcelo Ríos | 4–6, 4–6, 3–6 |
| Runner-up | 5 May 1997 | Munich, Germany | Clay | Mark Philippoussis | 6–7, 6–1, 4–6 |
| Winner | 19 May 1997 | Rome, Italy | Clay | Marcelo Ríos | 7–5, 7–5, 6–3 |
| Winner | 21 July 1997 | Stuttgart Outdoor, Germany | Clay | Karol Kučera | 6–2, 7–5 |
| Winner | 16 February 1998 | Dubai, UAE | Hard | Félix Mantilla Botella | 7–6 (7–0) , 6–0 |
| Runner-up | 11 May 1998 | Hamburg, Germany | Clay | Albert Costa | 2–6, 0–6, 0–1, ret. |
| Runner-up | 8 June 1998 | French Open , Paris, France | Clay | Carlos Moyà | 3–6, 5–7, 3–6 |
| Winner | 13 July 1998 | Gstaad, Switzerland | Clay | Boris Becker | 7–6 (7–5) , 7–5, 6–3 |
| Winner | 24 August 1998 | Indianapolis, U.S. | Hard | Andre Agassi | 2–6, 6–2, 6–3 |
| Winner | 26 October 1998 | Lyon, France | Carpet | Tommy Haas | 2–6, 7–6 (8–6) , 6–1 |
| Winner | 30 November 1998 | Tennis Masters Cup , Hanover, Germany | Hard | Carlos Moyà | 3–6, 3–6, 7–5, 6–3, 7–5 |
| Runner-up | 18 January 1999 | Sydney, Australia | Hard | Todd Martin | 3–6, 6–7 |
| Runner-up | 30 August 1999 | Long Island, U.S. | Hard | Magnus Norman | 6–7 (4–7) , 6–4, 3–6 |
| Runner-up | 20 September 1999 | Mallorca, Spain | Clay | Juan Carlos Ferrero | 6–2, 5–7, 3–6 |
| Winner | 20 March 2000 | Indian Wells, U.S. | Hard | Thomas Enqvist | 6–4, 6–4, 6–3 |
| Winner | 17 July 2000 | Gstaad, Switzerland | Clay | Mariano Puerta | 6–1, 6–3 |
| Winner | 30 July 2000 | Kitzbühel, Austria | Clay | Emilio Benfele Álvarez | 6–3, 6–1, 3–0 retired |
| Winner | 21 August 2000 | Washington, U.S. | Hard | Andre Agassi | 6–2, 6–3 |
| Winner | 23 October 2000 | Toulouse, France | Hard | Carlos Moyà | 6–3, 6–2 |
| Runner-up | 11 June 2001 | French Open , Paris, France | Clay | Gustavo Kuerten | 7–6 (7–3) , 5–7, 2–6, 0–6 |
| Winner | 23 July 2001 | Amsterdam, Netherlands | Clay | Younes El Aynaoui | 6–3, 5–7, 7–6 (7–0) , 3–6, 6–4 |
| Winner | 15 July 2002 | Gstaad, Switzerland | Clay | Gastón Gaudio | 6–3, 7–6 (7–3) , 7–6 (7–3) |
| Winner | 29 July 2002 | Kitzbühel, Austria | Clay | Juan Carlos Ferrero | 6–4, 6–1, 6–3 |
Question:
What type of surface did they play on 21 July 1997
Answer:
Clay