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".
Q: [header] How to choose an mp3 player to improve your english [title] Think on portability. [step] The selected device must be a flash memory-based mp3 player. It's the smallest and lightest and typically allows to store hundreds of audio files. <sep> (A) Portability costs a small sum of money, without varying the storage capacity. Potential choices include echo, track system, dvi, nw, samsung sync, or usr that the device supports. (B) It needs to be relatively small because some portable sound systems only record one video file per second and others have bigger files than others. Select video files that are named as' flash memory' and choose decimal places for the number. (C) Because it's small and contains no moving parts, it's ideal for carrying while exercising. Generally flash memory-based mp3 players fit in a pocket. (D) Choose a hard drive and a usb flash player if needed. High end laptops have hard disks which must be taken out from a hardware-disposal site to format.
A:
C