Most likely audience and purpose. It's not like there are timed applications and the way you write it is up to as long as it makes sense.
Good scientific writing is clear
it avoids unnecessary detail and simple
it uses direct language
avoiding vague or complicated sentences.
I think it would be
Communism
' C ' has the misplaced modifier. It makes the sentence sound like the commands take the obedience class.
It should say "The dogs that take the obedience class know several commands.".
