$\displaystyle \int _ {0} ^ {1} {\left (\frac{1} {\sqrt {4-x ^ {2}}} + \sqrt {1-x} \right)} dx$ 의 값은?

• ①$\displaystyle \frac{\pi} {12} + \frac{1} {2}$
• ②$\displaystyle \frac{\pi} {12} + \frac{2} {3}$
• ③$\displaystyle \frac{\pi} {6} + \frac{1} {3}$
• ④$\displaystyle \frac{\pi} {6} + \frac{1} {2}$
• ⑤$\displaystyle \frac{\pi} {6} + \frac{2} {3}$