问题如下：
An investment banking department of a brokerage firm often receives material nonpublic information that could have considerable value if used in advising the firm’s brokerage clients. In order to conform to the Code and Standards, which one of the following is the best policy for the brokerage firm?
选项：
A. Permanently prohibit both "buy" and "sell" recommendations of the stocks of clients of the investment banking department.
B. Establish physical and informational barriers within the firm to prevent the exchange of information between the investment banking and brokerage operations.
C. Monitor the exchange of information between the investment banking department and the brokerage operation.
解释：
B is correct.
The best policy to prevent violation of Standard II(A) –Material Nonpublic Information is the establishment of firewalls in a firm to prevent exchange of insider information. The physical and informational barrier of a firewall between the investment banking department and the brokerage operation prevents the investment banking department from providing information to analysts on the brokerage side who may be writing recommendations on a company stock. Prohibiting recommendations of the stock of companies that are clients of the investment banking department is an alternative, but answer A states that this prohibition would be permanent, which is not the best answer. Once an offering is complete and the material nonpublic information obtained by the investment banking department becomes public, resuming publishing recommendations on the stock is not a violation of the Code and Standards because the information of the investment banking department no longer gives the brokerage operation an advantage in writing the report. Answer C is incorrect because no exchange of information should be occurring between the investment banking department and the brokerage operation, so monitoring of such exchanges is not an effective compliance procedure for preventing the use of material nonpublic information.
老师请问，监控两个部门的股票交易也是无效的，对吧？可以解释一下原因吗？