Two identical springs are attached to a small block\[p\]. The other ends of the springs are fixed at \[A\] and\[B\]. When \[p\]the extension of top spring is in equilibrium is 20 cm and extension p of bottom spring is 10 cm. The period of small vertical oscillations of? about its equilibrium position is (use \[g=9.8\,m/{{s}^{2}}\])

• A. \[\frac{2\pi }{7}\sec \]               
• B. \[\frac{\pi }{7}\sec \]
• C. \[\frac{2\pi }{5}\sec \]   
• D. none of these