You will be given a definition of a task first, then some input of the task.
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 set macgo mac blu ray player as default player [title] Download mac blu-ray menu player and install it at once. [step] There will be watermark on your screen if you play blu-ray with the trial version. Only 39.95 dollars for the full version of mac blu-ray menu player for now, please buy mac blu-ray player with discount. <sep> (A) [title] Click " check file associations " under " tools ". [title] Click and macgo mac blu-ray player will be your default player. (B) [title] Choose your video size and port size from the dropdown menu at the top of mac blu-ray menu. [step] Once you have downloaded the blu-ray menu player and installed it, you have to choose your video size and port size. (C) [title] Run the make app and then the itunes installer. [title] Determine the output type for each file in your mac blu-ray player. (D) [title] Uncheck the sidebar at the bottom of " applications ". [step] These are the files that are currently currently on your mac blu-ray player.
Output:
A