Given the task definition and input, reply with output. In this task, you are given a context and four options. Each option is a suggested ending for the context. You should read the context and pick the best ending for the context. Please answer with "A", "B", "C", and "D".

[header] How to use a pendulum [title] Know that a pendulum is a weight hanging freely at the end of a string. [step] Before you start using a pendulum, you need to know what it is and how it works. Luckily, a pendulum is no more than a hanging weight allowed to swing back and forth. <sep> (A) If you store a pendulum by its string on your porch, anyone who walks by will know you have a pendulum, which can cause immediate deaths. [substeps] Lay a heavy book on the floor so that it sits flat. (B) The string is attached to a fixed point so that only the weight and string are moving. [substeps] Hold the end of pendant necklace or yo-yo between your fingers and move the " weight " at the bottom. (C) It can be hung anywhere from one level of the sky to the next. [title] Get your hands on a weighted pendulum. (D) Pendulum apabinus pendulum staff staff is a medium pendulum and floats with one side as horizontal as the other if viewed from at an angle. [title] Use the pendulum to increase your mobility in any given space.
B