If \(\overrightarrow a \) and \(\overrightarrow b\) are two unit vectors inclined to x - axis at angles 30° and 120°, then \(\left| {\overrightarrow a + \overrightarrow b } \right|\) equals

• A. \(\sqrt {\frac{2}{3}} \)
• B. \(\sqrt 2 \)
• C. √3
• D. 2