Question:
Which position did Stanislav Gross hold in Sep, 1999?

Context:
 Stanislav Gross holds the position of Minister of the Interior of the Czech Republic from Apr, 2000 to Aug, 2004. 
 Stanislav Gross holds the position of Member of the Chamber of Deputies of the Parliament of the Czech Republic from Jun, 2002 to Sep, 2004. 
 Stanislav Gross holds the position of chairperson from Jun, 1998 to Apr, 2000. 
 Stanislav Gross holds the position of Prime Minister of the Czech Republic from Aug, 2004 to Apr, 2005. 
 Stanislav Gross holds the position of Deputy Prime Minister of the Czech Republic from Jun, 2002 to Aug, 2004. 
 Stanislav Gross holds the position of member of the Czech National Council from Jun, 1992 to Dec, 1992. 
 Stanislav Gross holds the position of party leader from Mar, 2005 to Sep, 2005.

Answer:
chairperson