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:
| Drop(s) | Multiplayer Map(s) | Spec Ops Mission(s) | Face Off Map(s) | Xbox 360 release date | PlayStation 3 release date |
| --- | --- | --- | --- | --- | --- |
| 1-2 | Liberation & Piazza | None | None | 24 January 2012 | 28 February 2012 |
| 3 | Overwatch | None | None | 21 February 2012 | 29 March 2012 |
| 4-6 | Black Box | Black Ice & Negotiator | None | 13 March 2012 | 12 April 2012 |
| 7-8 | Sanctuary & Foundation | None | None | 10 April 2012 | 10 May 2012 |
| 9-12 | Oasis | Iron Clad & Kill Switch | Getaway & Lookout | 15 May 2012 | 14 June 2012 |
| 13-15 | None | Arctic Recon | Vortex, U-Turn & Intersection | 19 June 2012 | 19 July 2012 |
| 16-18 | Decommission & Offshore | Vertigo | None | 17 July 2012 | 16 August 2012 |
| 19-21 | None | Special Delivery, Light 'Em Up & Special Ops Chaos Mode | None | 7 August 2012 | 6 September 2012 |
| 22-24 | Parish, Gulch & Boardwalk | None | None | 5 September 2012 | 9 October 2012 |
Question:
which drop(s) had the most spec ops mission(s)?
Answer:
19-21