@willpassby2014, I answered A as well but I wasn't satisfied with Ninja MCQ's answer so I looked it up.
I believe the auditor and management set the limits of materiality for which management will communicate to the lawyer for purposes of the ‘letter of inquiry' (See AU-C 501.A56 and AU-C 501.A69 for example). However the lawyer can establish his/her test of materiality. The lawyer should also reach an understanding of materiality with auditor regarding materiality to be used in response.
“If the audit inquiry sets forth a definition of materiality but the lawyer utilizes a different test of materiality, he should specifically so state. The lawyer may wish to reach an understanding with the auditor concerning the test of materiality to be used in his response, but he need not do so if he assumes responsibility for the criteria used in making materiality determinations. Any such understanding with the auditor should be referred to or set forth in the lawyer's response. In this connection, it is assumed that the test of materiality so agreed upon would not be so low in amount as to result in a disservice to the client and an unreasonable burden on counsel.” (See AU-C 501.A70)
AUD - 91
BEC - 84
FAR - 91
REG - 91