Final answer:
In June 1934, Hitler prevented an internal power struggle within the Nazi party in an event termed The Night of the Long Knives. This was distinct from the Beer Hall Putsch of November 1923, Operation Valkyrie in 1944, and Operation Barbarossa in 1941.
Step-by-step explanation:
In June 1934, Adolf Hitler took action to stop an attempted coup within Nazi Germany by a paramilitary group. The event you are referring to is known as D. The Night of the Long Knives. During this event, Hitler ordered the execution of many of the leaders of the Sturmabteilung (SA), the Nazi Party's own paramilitary organization, to consolidate his power and appease the German military, which viewed the SA with growing concern. This was not to be confused with the Beer Hall Putsch in November 1923, which was Hitler's earlier failed coup attempt in Munich. The other options you have mentioned, such as Operation Valkyrie, were a plot against Hitler's life in 1944, and Operation Barbarossa, which was the code name for the German invasion of the Soviet Union in 1941.