The area of the triangle whose vertices are $A(1, 1, 1)$,$B(1, 2, 3)$,and $C(2, 3, 1)$ is . . . . . . sq. units.

  • A
    $\frac{19}{2}$
  • B
    $\frac{\sqrt{21}}{2}$
  • C
    $\frac{21}{2}$
  • D
    $\frac{\sqrt{19}}{2}$

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