(You can try these, these words can represent "system".) Method or methods, organization, routine, strategy, or operation.
The answer would be (A) again because in a essay you are stating your points and you have a structure on how to do it and it must be consistent throughout the whole essay or its going to be choppy and you wont get a good grade. hopefully that made sense. The other answers wouldn't make sense. So go with (A)
The type of verbal is participle and the verbal phrase is “playing the piano”
