Rebuttal is the idea or opinion that means the opposes a counterclaim.
Answer is C. Rebuttal.
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Answer:
People who study codes
Explanation:
The sentence that gave it away is If there were no cribs to be found, the British would send out false information about, say, British mines planted in a given area. The Germans might then send messages with the name of that area, which would provide clues about deciphering that code. 
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C because a market research helps when you are buying something which he is (car) and this is a secondary resource because it is recommended by someone rather than them finding the research himself.