题目内容
（请给出正确答案）
[主观题]
The Forbidden City in Beijing is listed by UNESCO as the largest collection of preserved in the world.
A、ancient wooden structure
B、ancient golden structure
C、ancient woolen structure
D、ancient brick structure
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为从代数系(Z,+)到代数系（Z,
)的同构，这里Z为整数集，+为整数的加法运算，
,则
=()。
