关于ios 往可变字典添加object会覆盖到上一个key的值啊！怎么解决！

self.arr=[NSMutableArray new];
self.dic=[NSMutableDictionary new];
[self.arr addObjectsFromArray:@[@"1",@"2",@"3"]];
[self.dic setObject:self.arr forKey:@"key1"];
[self.arr removeAllObjects];
[self.arr addObjectsFromArray:@[@"3",@"4",@"5"]];
[self.dic setObject:self.arr forKey:@"key2"];

NSLog(@"%@",self.dic);



    输出结果：
    {
key1 =     (
    3,
    4,
    5
);
key2 =     (
    3,
    4,
    5
);
}