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 buy a ceiling fan [title] Measure the length and width of the room. [step] Before you go ahead and buy your new ceiling fan, there are a number of factors and variables that you need to take into account. The first of these is the size of the room you are buying the fan for. <sep> (A) The size of the room a fan fits comfortably in. [substeps] Take the height and width of the room into account. (B) [substeps] Ideally, the ceiling fan should be at least as wide as the room's ceiling area. However, in large rooms, it can be as wide as the space between the ceiling opening and the wall of the room. (C) Calculate these by weighing the ceiling fan at a traditional estimate of its height and width. [substeps] Btus is the height of the ceiling fan's widest edge (known as the flat edge). (D) To make sure that the fan works effectively you need to ensure that it is big enough for the space. [substeps] Get hold of a tape measure and determine the length and width of the room.
D