Question: In September 1939, when the Second World War begun, the then General Alfred Keller commanded the 4th Air Corps during the invasion of which countrty, he commanded Luftflotte 2, with his superior General Albert Kesselring, was a German "Luftwaffe Generalfeldmarschall" during World War II?

full_context: Document 1: Erwin Rommel: Erwin Rommel (15 November 1891 – 14 October 1944) was a German general and military theorist. Popularly known as the Desert Fox, he served as field marshal in the Wehrmacht of Nazi Germany during World War II.
Document 2: Norwegian Campaign order of battle: The German operation for the invasion of Denmark and Norway in April 1940 was code-named "Weserübung", or "Weser Exercise." Opposing the invasion were the partially mobilized Norwegian military, and an allied expeditionary force composed of British, French, and Free Polish formations. The following list formed the order of battle for this campaign.
Document 3: Afrika Korps: The Afrika Korps or German Africa Corps (German: "Deutsches Afrikakorps" , DAK    </small>) was the German expeditionary force in Africa during the North African Campaign of World War II. First sent as a holding force to shore up the Italian defense of their African colonies, the formation fought on in Africa, under various appellations, from March 1941 until its surrender in May 1943. The unit's best known commander was Field Marshal Erwin Rommel.
Document 4: Werner Schröer: Werner Schröer (12 February 1918 – 10 February 1985) was a German World War II fighter ace who served in the "Luftwaffe" from 1937, initially as a member of the ground staff, until the end of World War II in Europe on 8 May 1945, by which time he had reached the highest ranks of combat leadership. A flying ace or fighter ace is a military aviator credited with shooting down five or more enemy aircraft during aerial combat. Schröer was also a recipient of the Knight's Cross of the Iron Cross with Oak Leaves and Swords. The Knight's Cross of the Iron Cross and its higher grade Oak Leaves and Swords was awarded to recognise extreme battlefield bravery or successful military leadership. For the fighter pilots, the grades of the Knight's Cross were also a quantifiable measure of their success and skill. Werner Schröer was the second most successful claimant of air victories after Hans-Joachim Marseille in the Mediterranean.
Document 5: Manfred von Richthofen (general): Karl Ernst Manfred Freiherr von Richthofen (24 May 1855 – 28 November 1939) was a German "General der Kavallerie" (General of the Cavalry) during World War I and recipient of the order Pour le Mérite, known informally as the Blue Max. Richthofen was a great uncle of his more famous namesake Manfred von Richthofen, known as the Red Baron, who was his godson and named after him.
Document 6: 9th Air Division (Germany): 9. Flieger-Division (9th Air Division) was one of the primary divisions of the German Luftwaffe in World War II. The division was founded on 1 February 1940 in Jever and initially subordinated to the Oberkommando der Luftwaffe (OBdL). On 23 May 1940 the division was subordinated to the Luftflotte 2 and transferred to Soesterberg in July 1940. The unit was redesignated "IX. Fliegerkorps" in November 1940.
Document 7: Erich Hartmann: Erich Alfred Hartmann (19 April 1922 – 20 September 1993), nicknamed "Bubi" ("The Kid") by his German comrades and "The Black Devil" by his Soviet adversaries, was a German fighter pilot during World War II and the most successful fighter ace in the history of aerial warfare. He flew 1,404 combat missions and participated in aerial combat on 825 separate occasions. He claimed, and was credited with, shooting down 352 Allied aircraft—345 Soviet and 7 American—while serving with the "Luftwaffe". During the course of his career, Hartmann was forced to crash-land his fighter 14 times due to damage received from parts of enemy aircraft he had just shot down or mechanical failure. Hartmann was never shot down or forced to land due to enemy fire.
Document 8: Günther Rall: Günther Rall (10 March 1918 – 4 October 2009) was a German lieutenant-general, the third most successful fighter ace in history and later head of the West German Luftwaffe during the Cold War.
Document 9: Kurt Pflugbeil: Kurt Leopold Pflugbeil (9 May 1890 – 31 May 1955) was a German general (General der Flieger) in the Luftwaffe during World War II who commanded 4th Air Corps and Luftflotte 1. He was a recipient of the Knight's Cross of the Iron Cross with Oak Leaves of Nazi Germany.
Document 10: Alfred Keller: In September 1939, when the Second World War begun, the then General Alfred Keller commanded the 4th Air Corps during the invasion of Poland, assuming this command on 13 October 1939. The following campaigns, during campaigns against Norway, the Netherlands, Belgium and the Battle of France, he commanded Luftflotte 2 with General Albert Kesselring as his superior.
Document 11: Albert Praun: Praun served during World War I. He was retained in the Reichswehr and then served in the Wehrmacht; between 1935 and 1940 he commanded signals units. In 1940 he was then appointed Chief Signals Officer of Panzer Group Hoth and Panzer Group Guderian in France. He was then posted to the Eastern Front where he served as Chief Signals Officer of the 2nd Panzer Group. He later was the commanding officer of the 4th Panzer Grenadier Brigade and then of the 18th Panzer Division, and the 129th and the 277th Divisions.
Document 12: Luftwaffe Order of Battle August 1940: For its Battle of Britain campaign against Great Britain during World War II, the German Luftwaffe had the following Order of Battle in the West. "Luftflotte 2" was responsible for the bombing of southeast England and the London area and based in the Pas-de-Calais area in France. "Luftflotte 3" targeted the West Country, Midlands, and northwest England, from bases a bit further north in France. "Luftflotte 5" targeted the north of England and Scotland, from bases in Norway. "Luftflotte 1" and "Luftflotte 4" were based in Germany, but most of their bomber formations had been reassigned to the three "Luftflotten" engaged in the Battle of Britain. Some fighters were retained to provide air cover over Germany, however.
Document 13: Adolf Dickfeld: Adolf Dickfeld (20 February 1910 – 17 May 2009) was a World War II Luftwaffe officer and 136 victories Flying ace. A flying ace or fighter ace is a military aviator credited with shooting down five or more enemy aircraft during aerial combat. He was also a recipient of the Knight's Cross of the Iron Cross with Oak Leaves (German: "Ritterkreuz des Eisernen Kreuzes mit Eichenlaub" ). The Knight's Cross of the Iron Cross and its higher grade Oak Leaves was awarded to recognise extreme battlefield bravery or successful military leadership.
Document 14: Helmuth Förster: Helmuth Förster (19 April 1889 – 7 April 1965) was a German general' in the Luftwaffe during World War II. A decorated World War I aviator, he returned to military service in 1934 as an "Oberstleutnant" in the Luftwaffe. Promoted to "Oberst" in 1936, he was appointed to command the 4th Bomber Wing. During the invasion of Poland, Förster commanded the "Lehrdivision" with significant success. He was then appointed as chief of staff of the 5th Air Fleet during the invasion of Norway. After serving on the German-French Peace Commission, he was appointed as military governor of the German-occupied territory of Serbia from April to June 1941, then commanded the 1st Air Corps during the invasion of the Soviet Union until October 1942. Whilst in command of the 1st Air Corps he was awarded the Knight's Cross of the Iron Cross. He spent the remainder of the war as chief of administration at the Reich Ministry of Aviation. He was pensioned as an "Oberstleutnant" in 1952.
Document 15: Albert Kesselring: Albert Kesselring (30 November 1885 – 16 July 1960) was a German "Luftwaffe Generalfeldmarschall" during World War II. In a military career that spanned both World Wars, Kesselring became one of Nazi Germany's most skilful commanders, and one of the most highly decorated, being one of 27 soldiers awarded the Knight's Cross of the Iron Cross with Oak Leaves, Swords and Diamonds. Nicknamed "Smiling Albert" by the Allies and "Uncle Albert" by his troops, he was one of the most popular generals of World War II with the rank and file.
ground_truth: Poland