Answer:
The excerpt that supports the idea that Allied forces expected the Germans to complicate their coding system is:
C. 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.
Step-by-step explanation:
According to excerpt C, the Allies were already one step ahead. Because they already expected Germans to complicate their coding system, British and Polish cryptologists found different ways to recover the daily keys. And they were right. Germans eventually did begin to use new rotors and plugs with the purpose of creating more combinations. However, when that happened, cryptologists had already figured out their alternative methods.