[tex]A\ volume\ of\ a\ square\ pyramid:\\\\V=\dfrac{1}{3}a^2H\\\\a-length\ of\ a\ side\ of\ a\ base\\H-a\ height\ of\ a\ pyramid\\-------------------\\a=s;\ H=\dfrac{1}{2}s\\\\subtitute\\\\V=\dfrac{1}{3}s^2\cdot\dfrac{1}{2}s=\dfrac{1}{6}s^3\\\\\boxed{V=\frac{1}{6}s^3}\to\fbox{B.} [/tex]
