求解释VBA代码

从for开始帮忙解释下啊~~谢谢
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Sub 保存()
Dim arr, brr, d, i&
Set d = CreateObject("scripting.dictionary")
Sheet1.Activate
arr = Range("a10").CurrentRegion
brr = Sheet2.Range("a1").CurrentRegion
For i = 2 To UBound(arr)
d(arr(i, 7)) = i + 9
Next
For i = 2 To UBound(brr)
If d.exists(brr(i, 7)) Then Rows(d(brr(i, 7))).Copy Sheet2.Cells(i, 1)
Next
MsgBox "保存完毕!"
End Sub
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