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Baoding Ermo 20 17 Mathematics Volume
B is BM⊥x axis and BN⊥y axis, as shown in the figure:

∴M and n are the midpoint of α and α respectively,

∴AN=ON,OM=CM,

∫A(0,2),

∴OA=2,

Similarly, the quadrilateral BMON is rectangular,

∴ON=BM= 1,

∫∠ODC = 60,

∴∠OBC= 120,

And ∵BO=CO, BM⊥OC,

∴∠OBM=60,

In Rt△OBM, BM= 1,

So OM=BM? tan60 =3,

Then oc = 2om = 23.

So choose d