If \(\rm \vec{a} \ and\ \vec b\) are two vectors such that \(\rm | \vec{a}| = \frac{1}{\sqrt3} \ , |\vec b| = 2\) and \(\rm \vec{a}\times \vec{b}\) is a unit vector, then find the angle between \(\vec a \ and \ \vec b\)

• A. 30°
• B. 90°
• C. 45°
• D. 60°