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```

NSMutableString* mt1 = [NSMutableStringstringWithString:@"tttt"];

NSMutableString* mt2 = @"hhhh";

NSLog(@"%p",mt1);

NSLog(@"%@", mt1.class);

NSLog(@"%@", mt2.class);

[mt1 appendString:@"fff"];

[mt2 appendString:@"fff"];

NSLog(@"%p",mt1);

NSLog(@"%p",mt2);

```