Answer: one of the biggest impacts are probably trading between countries. (Possibly incorrect)
Orwell uses Boxers decision to avoid mor carnage by working hard to show how the working class was manipulated
The fragment that is made up of a complete predicate is option A. "could not be heard above the voices in the hallway"
In grammar, the predicate is defined as the part of the sentence that contains the verb and gives information about the subject.
Option A is the only option that contains a verb, in this case "could" and it is providing information about a subject we don´t know. The only options lack verbs,
The answer is the last one, D. All of the other transitions indicate that the writer will either go into further detail on the subject or list other reasons as to why this would be correct. However, D clearly uses a contrasting transition to introduce a new argument.