Q: 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 fireproof a bedroom [title] Install a smoke alarm in the bedroom. [step] The smoke alarm should be located in an easily accessible location, so that you can practice proper maintenance. You need to replace the batteries on the smoke detector every six months. <sep> (A) You will also need an air purifier under your bed. [substeps] There are different types of air purifiers. (B) [title] Install smoke sensors at the thermostat. [step] The sensors can hold smoke in and out of the room at the correct temperature. (C) [substeps] There are 2 main types of smoke alarms. Test one and replace it every 6 months. (D) Since smoke alarm sensitivity reduces with age, you should replace the alarm periodically. You should not use a smoke alarm that is older than ten years.
A:
D