How to transform position of object A to object C (C is a child of B object)

How to transform position of object A to object C (C is a child of B object)

I try using transform.position but the child position and the object outside parent position are not the same.

Since object C is a child of object B, set the position of object A to object B. Or you could set object A to a child of object B, then set the transform the same as object C, then finally unset object A’s parent.
If you need an example script please let me know!