A、A growing donkey population. B、The wider use of horses. C、A shrinking animal trade. D、The arrival of tractors. D题目问的是骡子在美国需求变少

Do you know where a mule comes from? It is the child of a donkey and a horse.
    [22]Mules have strong muscles like horses but they eat less, can work longer, and are gentler, like donkeys.
    George Washington was the first person in the United States to own mules. He had heard that mules made good farm animals and he contacted the U.S. ambassador in Spain to ask about them. [23]In 1785, King Charles III of Spain sent Washington a male donkey as a gift. That male donkey became the father of the mule industry in the U.S.
    Every April, Maury County holds a Mule Day celebration. Held in Columbia, Tennessee, Mule Day had its beginning as "Breeder’s Day" in the 1840s. [24]Farmers and farm animal breeders would bring their animals to market every April to show, buy, and trade. This was an important business before the days of tractors, when many families made a living from farming and mules were used as work animal. [25]Eventually, tractors began to replace mules, making them less in demand.
    A parade was added to Mule Day in 1934 to attract more people. Over the years other activities have been added, and today more than 200,000 people show up each year to watch and participate. If you visit during Mule Day Celebrations, you might see mule-driving contests, square dances, or shows, or even tree-cutting competition.
22. What does the speaker say about mules’!
23. What do we learn about the donkey which is said to be the father of the US mule industry?
24. What did farmers usually do on Mule day in the 1840s?
25. What made mules less in demand in America?