If \(\vec a,\;\vec b\) and \(\vec c\) are the position vectors of the vertices of an equilateral triangle whose orthocentre is at the origin, then which one of the following is correct?

• A. \(\vec a + \vec b + \vec c = \vec 0\)
• B. \(\vec a + \vec b + \vec c =\) unit vector
• C. \(\vec a + \vec b = \vec c\)
• D. \(\vec a = \vec b + \vec c\)