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:
| № | # | Title | Directed by | Written by | Original air date | Production code | U.S. viewers (millions) |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 57.0 | 1.0 | " The Freshman " | Joss Whedon | Joss Whedon | October5,1999 | 4ABB01 | 5.8 |
| 58.0 | 2.0 | " Living Conditions " | David Grossman | Marti Noxon | October12,1999 | 4ABB02 | 6.4 |
| 59.0 | 3.0 | " The Harsh Light of Day " | James A. Contner | Jane Espenson | October19,1999 | 4ABB03 | 5.9 |
| 60.0 | 4.0 | " Fear, Itself " | Tucker Gates | David Fury | October26,1999 | 4ABB04 | 5.8 |
| 61.0 | 5.0 | " Beer Bad " | David Solomon | Tracey Forbes | November2,1999 | 4ABB05 | N/A |
| 62.0 | 6.0 | " Wild at Heart " | David Grossman | Marti Noxon | November9,1999 | 4ABB06 | 5.8 |
| 63.0 | 7.0 | " The Initiative " | James A. Contner | Douglas Petrie | November16,1999 | 4ABB07 | N/A |
| 64.0 | 8.0 | " Pangs " | Michael Lange | Jane Espenson | November23,1999 | 4ABB08 | N/A |
| 65.0 | 9.0 | " Something Blue " | Nick Marck | Tracey Forbes | November30,1999 | 4ABB09 | N/A |
| 66.0 | 10.0 | " Hush " | Joss Whedon | Joss Whedon | December14,1999 | 4ABB10 | 5.9 |
| 67.0 | 11.0 | " Doomed " | James A. Contner | Marti Noxon & David Fury & Jane Espenson | January18,2000 | 4ABB11 | N/A |
| 68.0 | 12.0 | " A New Man " | Michael Gershman | Jane Espenson | January25,2000 | 4ABB12 | N/A |
| 69.0 | 13.0 | " The I in Team " | James A. Contner | David Fury | February8,2000 | 4ABB13 | N/A |
| 70.0 | 14.0 | " Goodbye Iowa " | David Solomon | Marti Noxon | February15,2000 | 4ABB14 | N/A |
| 71.0 | 15.0 | " This Year's Girl " (Part 1) | Michael Gershman | Douglas Petrie | February22,2000 | 4ABB15 | N/A |
| 72.0 | 16.0 | " Who Are You " (Part 2) | Joss Whedon | Joss Whedon | February29,2000 | 4ABB16 | 5.5 |
| 73.0 | 17.0 | " Superstar " | David Grossman | Jane Espenson | April4,2000 | 4ABB17 | N/A |
| 74.0 | 18.0 | " Where the Wild Things Are " | David Solomon | Tracey Forbes | April25,2000 | 4ABB18 | N/A |
| 75.0 | 19.0 | " New Moon Rising " | James A. Contner | Marti Noxon | May2,2000 | 4ABB19 | 4.6 |
| 76.0 | 20.0 | " The Yoko Factor " (Part 1) | David Grossman | Douglas Petrie | May9,2000 | 4ABB20 | 4.9 |
| 77.0 | 21.0 | " Primeval " (Part 2) | James A. Contner | David Fury | May16,2000 | 4ABB21 | 5.2 |
Question:
What is the production code for the episode with 5.5 million u.s. viewers?
Answer:
4ABB16