Task: Question Answering
Input (English): 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.
Output (English): A