In WKB approximation, the quantization condition for two classical turning points is:
(A)
\int_{x_1}^{x_2} p(x) dx = \left(n + \frac{1}{2}\right) \pi \hbar
(B)
\int_{x_1}^{x_2} p(x) dx = n \pi \hbar
(C)
\int_{x_1}^{x_2} p(x) dx = \left(n + \frac{1}{4}\right) \pi \hbar
(D)
\int_{x_1}^{x_2} p(x) dx = 2n \pi \hbar