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:
| Date | City | Opponent | Results¹ | Type of game |
| --- | --- | --- | --- | --- |
| April 4 | Split | Netherlands | 2:0 | Euro 72' qualifier |
| April 21 | Novi Sad | Romania | 0:1 | Friendly |
| May 9 | Leipzig , Germany | East Germany | 2:1 | Euro 72' qualifier |
| July 18 | Rio de Janeiro , Brazil | Brazil | 2:2 | Friendly |
| September 1 | Budapest , Hungary | Hungary | 1:2 | Friendly |
| September 22 | Sarajevo | Mexico | 4:0 | Friendly |
| October 16 | Belgrade | East Germany | 0:0 | Euro 72' qualifier |
| October 27 | Podgorica | Luxembourg | 0:0 | Euro 72' qualifier |
Question:
When did the city of Novi Sad participate?
Answer:
April 21