阅读短文，从方框中选择适当的动词，并用其适当形式填空。有的需要加助动词或不定式符号。（每词限用一次）

    Last weekend, Jim went to see a film. It was about a boy ____ Bob. Bob lived with his parents in a small town. They were very poor. Bob's father ____  in a market for a long time. Bob wanted ____ a bike very much.
    One day, an old man ____ down by some boys, and they ran away. Bob went to help the old man. The old man gave him a magic book and told Bob to make a wish before opening it.
    Can you guess what ____  in the end? Please watch the film and find out!

①“换客”是一种商品流通

②“换客”可以使商品的价值最大化

③“换客”可以使商品的使用价值最大化

④“换客”有助于人们树立科学合理的消费

某商品涨价30%后欲恢复原价，则必须下降的百分数约为（　　）