Let \(\left| {\vec a} \right| \ne 0,\left| {\vec b} \right| \ne 0.\)\(\left( {\vec a + \vec b} \right).\left( {\vec a + \vec b} \right) = {\left| {\vec a} \right|^2} + {\left| {\vec b} \right|^2}\)Holds if and only if

• A. \(\vec a\) and \(\vec b\) are perpendicular
• B. \(\vec a\) and \(\vec b\) are parallel
• C. \(\vec a\) and \(\vec b\) are inclined at an angle of 45°
• D. \(\vec a\) and \(\vec b\) are anti-parallel