Ms. Fleming's class sets up an experiment involving pendulums. You can see in the picture that a pendulum is a "bob" attached to a string which hangs from a fixed point, allowing the bob to swing back and forth. They hook a 10 gram bob to a 12 inch string, and measure the time it takes for the bob to swing back and forth one time as 2 seconds. Then the class hooks a 10 gram bob to a 20 inch string and measure the time it takes to swing back and forth as 4 seconds. Lastly, the class hooks a 10 gram bob to a 30 inch string and measures its swing time. What is the best prediction of the last bob's swing time? A) 1 second. B) 2 seconds. C) 4 seconds. D) 6 seconds.