Answer:
The Germans would then find a different way of transmitting their messages.
Explanation:
According to a different source, this is the passage that comes with this question:
"Arthur Zimmermann had no idea that "Blinker" Hall had read his secret message. But now that Hall had read it, what could he do with this information? On one hand, he believed that President Wilson, faced with the information in the telegram, would declare war on Germany. On the other hand, to share the telegram with Wilson would surely alert Berlin that the British had been reading their secret messages. As he walked back to his office, Hall considered ways that he could share the intelligence in the Zimmermann telegram and establish its authenticity without letting Berlin know that Room 40 had intercepted and read hundreds of their secret messages."
This is the statement that best describes the reason why Hall was concerned that the Germans would learn the British were reading their secret messages. Hall believed that the information he had intercepted was very important, and that President Wilson should be made aware of this situation. However, he was also worried that, if the Germans learned about the reading of their messages, they would find another way of communicating, which would make the British unable to intercept the messages once more.
