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.

Answer 1

"The Russian admiralty decided that their British allies could make better use of the codebook than they could, so it was sent to London."

This sentence directly states that the Russians believed the British could make better use of the codebook, implying the British had superior code-breaking ability.