Given the task definition and input, reply with output. You are given an elementary science question along with a few answer options. List all the words from the question that are essential and sufficient for choosing the correct answer option. Keep in mind that essential words are necessary to understand the meaning of the given question. However, non-essential words provide little information needed to select the correct answer. You can think about it like this: If the question was in another language, knowing the meaning of which words were necessary and enough for you to understand the question and answer it?. If your answer consists of multiple spans of words from the question, separate those using a comma (", "). Do not generate any word that is not present in the question. Make sure that your response is contained in the given question and the words are in the same order as the question.
Grammatical correctness is not important.

Question: Which is the best explanation for how air masses move across the United States? (A) The prevailing westerlies move air masses from west to east across the United States but may be deflected by the jet stream. (B) The trade winds move air masses from west to east across the United States. (C) The jet stream moves air masses from the Pacific Ocean across the United States. (D) The warm air of the Gulf Stream causes air masses to move from the Atlantic Ocean to the Pacific Ocean.?
explanation, air, masses, move, United, States?