Let
P−ABC
be a tetrahedron whose edges have a length of 6 . If points
D,E,F
are the barycenter of triangles
△PAB,△PBC,△PAC
respectively, then the volume of the trigonal pyramid
P−DEF
is ( ).

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Let
P−ABC
be a tetrahedron whose edges have a length of 6 . If points
D,E,F
are the barycenter of triangles
△PAB,△PBC,△PAC
respectively, then the volume of the trigonal pyramid
P−DEF
is ( ). (A)
3
4
2
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(B)
3
2
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(C)
2
3
2
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(D)
2
2
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(E)
4
2
​