Đáp án:

\( \vec{u}_1 = (1, -1, 2), \quad \vec{u}_2 = (1, 1, 1). \)

\( \cos \varphi = \left| \cos(\vec{u}_1, \vec{u}_2) \right| = \frac{\left| \vec{u}_1 \cdot \vec{u}_2 \right|}{|\vec{u}_1| \cdot |\vec{u}_2|} = \frac{\left| -1 -1 +2 \right|}{\sqrt{6} \cdot \sqrt{3}} = 0 \Rightarrow  \varphi = 90^\circ \Rightarrow \boxed{B} \)