The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence.
​The popularity of rivalries fueled the attraction of the game (base- ball) and caused it to become the national past time. The sport transformed from being a game of amateurs into a sport played by professionals. With that transformation, the innocence of baseball had been lost. 

Baseball （） to a professional sport.