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:
| No. in season | No. in series | Title | Directed by | Written by | Original air date | U.S. viewers (million) |
| --- | --- | --- | --- | --- | --- | --- |
| 1.0 | 69.0 | "Line of Departure" | John T. Kretchmer | Debra Fordham | March 6, 2011 | 4.2 |
| 2.0 | 70.0 | "Command Presence" | Carl Lawrence Ludwig | Karen Maser | March 13, 2011 | 3.3 |
| 3.0 | 71.0 | "Movement to Contact" | John T. Kretchmer | Rebecca Dameron | March 20, 2011 | 3.8 |
| 4.0 | 72.0 | "On Behalf of a Grateful Nation" | John Terlesky | T.J. Brady & Rasheed Newson | March 27, 2011 | 4.7 |
| 5.0 | 73.0 | "Soldier On" | Rob Spera | Bill Rinier | April 3, 2011 | 3.3 |
| 6.0 | 74.0 | "Walking Wounded" | Chris Peppe | James Stanley | April 10, 2011 | 3.4 |
| 7.0 | 75.0 | "Strategic Alliances" | Melanie Mayron | T.D. Mitchell | April 17, 2011 | 3.4 |
| 8.0 | 76.0 | "Supporting Arms" | Emile Levisetti | Mary Leah Sutton | May 1, 2011 | 3.1 |
| 9.0 | 77.0 | "Countermeasures" | James Bruce | Debra Fordham | May 8, 2011 | 3.3 |
| 10.0 | 78.0 | "Battle Buddies" | Brian McNamara | Tanya Biank | May 15, 2011 | 3.2 |
| 11.0 | 79.0 | "Drop Zone" | Rob Spera | James Stanley | May 22, 2011 | 3.6 |
| 12.0 | 80.0 | "Firefight" | John Terlesky | Rasheed Newson | June 5, 2011 | 3.4 |
Question:
Who wrote the episode that aired on April 17, 2011? 
Answer:
T.D. Mitchell