The piece of textual evidence that best supports the inference that the British had better code breakers than the Russians did is:
The codebook was a bonanza for the British code breakers.
What does the statement imply
This statement suggests that the British code breakers found the codebook highly valuable and successful in their code-breaking efforts.
The use of the term bonanza indicates that the British code breakers gained a significant advantage or windfall from the codebook, reinforcing the idea that they were more skilled or effective in deciphering the coded messages than the Russians.
complete question
Read the excerpt from The Dark Game.
The Russian admiralty decided that their British allies could make better use of the codebook than they could, so it was sent to London. The codebook was a bonanza for the British code breakers. Not only did it contain the columns of code "words"—groups of randomly selected numbers—on which the messages were based, but it also included a changeable key to the cipher systems used to obscure the coded messages.
Which piece of textual evidence best supports the inference that the British had better code breakers than the Russians did?
The Russian admiralty decided that their British allies could make better use of the codebook than they could, so it was sent to London.
The codebook was a bonanza for the British code breakers.
Not only did it contain the columns of code "words"—groups of randomly selected numbers—on which the messages were based
[B]ut it also included a changeable key to the cipher systems used to obscure the coded messages.