A U-tube of uniform bore holds a liquid column whose total length, measured along the tube, is $40\ \text{cm}$, as shown in the figure. The liquid in one arm is pushed down a little and then let go, so the liquid swings back and forth. Ignoring friction and taking $g = 10\ \text{m/s}^2$, the period of the oscillation is closest to

Fig. 1: A U-tube of liquid with the level x below its rest level in one arm and x above it in the other. The total length of the liquid column is 40 cm.