Question

began monitoring swedish cables. and it had all started with the keen observations of mr. h. now hall wondered if mr. h. could assist him again. he contacted his operative and made his request. then he waited for mr. h. to do his work. why did hall want to contact mr. h? hall wanted mr. h to intercept the telegram that von bernstorff was going to send to the german ambassador in mexico. hall wanted mr. h to report to woodrow wilson the findings of the zimmermann telegram. mr. h was a traitor and hall wanted to find mr. h to arrange an arrest. mr. h knew the meaning of secret codes that the people in room 40 could not decipher.

Explanation:

The text mentions Hall had started monitoring Swedish cables due to Mr. H's keen observations and now wanted his assistance again. This implies Mr. H has some special knowledge or ability relevant to the work. Among the options, the idea that Mr. H knew the meaning of secret - codes that others in Room 40 couldn't decipher aligns with the need for his assistance.

Answer:

Mr. H knew the meaning of secret codes that the people in Room 40 could not decipher.