Question

which excerpt from \the enigma machine\ supports the idea that allied forces expected the germans to complicate their coding system?
the enigma machine was invented at the end of world war i by german engineer arthur scherbius. he used rotors and an electrical pathway in his design.
the telegram was intercepted and deciphered by british intelligence, and it caused such outrage in the us that it helped generate public support for the united states entry into the war.
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.
the two main weaknesses of the enigma machine were careless operators and the distribution of the daily key. the daily key was printed on paper, and it had the potential of being captured en route to the field.

Explanation:

The third option shows that after the Germans made changes (introduced additional rotors and plugs to complicate the coding system), the Allied cryptologists (Polish and British) had already developed methods. This implies that the Allied forces were prepared for the Germans to complicate the system as they had alternative methods ready. The first option just tells about the invention of the Enigma machine. The second option is about a telegram and its impact. The fourth option is about the weaknesses of the Enigma machine.

Answer:

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.