public class MyLogger

单项选择题 public class MyLogger { private StringBuilder logger = new StringBuuilder（）； public void log（String message， String user） { logger.append（message）； logger.append（user）； } } The programmer must guarantee that a single MyLogger object works properly for a multi-threaded system. How must this code be changed to be thread-safe？（）: A、 synchronize the log method; B、 replace StringBuilder with StringBuffer; C、 No change is necessary， the current MyLogger code is already thread-safe.; D、 replace StringBuilder with just a String object and use the string concatenation （+=） within the log method

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