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"After 1938, when the Germans introduced additional rotors and plugs to increase the number of possible combinations, Polish and British cryptologists had already developed alternative methods of recovering the daily keys" is the excerpt which supports the idea that Allied forces expected the Germans to complicate their coding system. The essential part of this sentence is "...Polish and British cryptologists had already developed alternative methods...". Hope this helps!
The excerpt from "The Enigma Machine” that supports the central idea is that after 1938, when the Germans introduced additional rotors and plugs.
What is a central idea?
A central idea simply means the main idea that's in a literary work. It's the underlying message in the story.
In this case, the excerpt that supports the central idea is that after 1938, when the Germans introduced additional rotors and plugs to increase the number of possible combinations.
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