Task: Pos Tagging
Input (English): Sentence: It was recognized years ago that the transition {{ from }} daytime to nighttime propagation conditions , and vice versa , is not an instantaneous process , but takes place over periods of time from roughly 2 hours before sunset until about 2 hours after sunset , and again from roughly 2 hours before sunrise until some 2 hours after sunrise . 
Word: from
Output (English): ADP