Cho hình tứ diện ABCD có trọng tâm G . Mệnh đề nào sau đây là sai?

$A. \stackrel{\rightharpoonup }{GA} + \stackrel{\rightharpoonup }{GB} +\hspace{0.17em}\stackrel{\rightharpoonup }{GC} +\hspace{0.17em}\stackrel{\rightharpoonup }{GD} = 0$

$B. \stackrel{\rightharpoonup }{OG} = \frac{1}{4}(\stackrel{\rightharpoonup }{OA} + \stackrel{\rightharpoonup }{OB} +\hspace{0.17em}\stackrel{\rightharpoonup }{OC} +\hspace{0.17em}\stackrel{\rightharpoonup }{OD})$

$C. \stackrel{\rightharpoonup }{AG} = \frac{1}{4}(\stackrel{\rightharpoonup }{AB} + \stackrel{\rightharpoonup }{AC} +\hspace{0.17em}\stackrel{\rightharpoonup }{AD})$

$D. \stackrel{\rightharpoonup }{AG} = \frac{2}{3}(\stackrel{\rightharpoonup }{AB} + \stackrel{\rightharpoonup }{AC} +\hspace{0.17em}\stackrel{\rightharpoonup }{AD})$