[Vocabulary] "The verb," accompany"

[infiniteone]

"Each exercise is accompanied by a full answer key at the back of the book."

This is a sentence on the introduction page in a textbook.
Reading this, I've come to wonder why the writer used passive voice.

Why didn't he compose it like these:
"Each exercise accompanies full answer key at the back of the book." or " At the back of the book, full answer key accompanies each exercise."

Is there any difference in meaning among them?

I think the point is the diffrence between 'the first and the second', and between 'the first and the third'.

Thanks for reading this.

 

[Raymott]

"Each exercise is accompanied by a full answer key at the back of the book."

This is a sentence on the introduction page in a textbook.
Reading this, I've come to wonder why the writer used passive voice.

Why didn't he compose it like these:
"Each exercise accompanies full answer key at the back of the book." or " At the back of the book, full answer key accompanies each exercise."

Is there any difference in meaning among them?

I think the point is the diffrence between 'the first and the second', and between 'the first and the third'.

Thanks for reading this.

He could have written, " At the back of the book, a full answer key accompanies each exercise." But the main topic he's writing about are the exercises, not the answer keys.
And he wouldn't write, "Each exercise accompanies a full answer key", because the exercise is primary. Without the exercise, the answer key wouldn't be of much use. So, the answer key accompanies the exercise, not the other way around.

These two facts - the exercise being the current topic, and the exercise being the more important feature - explain why he expressed it as he did.