No change! this sentence is correct!
The preposition that is used in the given sentence above is the word "at", so the prepositional phrase is "at least once". Therefore, the words that are part of the prepositional phrase in this sentence are the words least and once. Hope this answers your question. Have a great day!
Answer:
While the newspaper makes some students more comfortable about speaking out against The Wave. Many of them reject The Wave since it did not help the football team win its big game against Clarksville. Mr. Ross notices that the other teachers seem to have turned against The Wave, something that is confirmed when Christy and Principal Owens confront him about it. However, he reassures his wife and boss that he has a plan to end the experiment gracefully, in a way that will teach the students about fascism. They agree, although Principal Owens threatens to fire Mr. Ross if the experiment continues to go awry.
Step-up transformers are used in the transmission of electrical energy by increasing the voltage for efficient long-distance transmission. Step-up transformers increases the voltage which will increase resistance at constant current. At a lower current value, transmission is much more efficient.