The correct answer is B. At Bletchley Park, the ten thousand people on the staff figured out over six thousand codes, some of which were very important to the war effort.
Step-by-step explanation:
In writing a summary refers to a brief account or compilation of the most important ideas or point developed in a paragraph or text. In the except presented the author explains in Britain and more specifically at Bletchley Park there were ten thousand workers trying to decipher around six thousand encoded messages and some of this messages had an important impact on the result of the war. This means the summary of this paragraph needs to include the more important details that are the place where the events occur, the number of messages and people that decipher them and the detail that some of them were crucial.
Therefore the best summary is " At Bletchley Park, the ten thousand people on the staff figured out over six thousand codes, some of which were very important to the war effort" because this includes the most important details presented in the text and does not modify or add the information of the original source.