[解析]
(1)B.理解推断题,根据最后一段We are tired," said Dalin. "but we gained a lot.""我们累了,"大林说,"但是我们收获了很多."可知作者对这些孩子的行为是持鼓励的态度的,故答案为:B.
(2)C.细节理解题,根据第四段Compared to traveling,such social practice connects us and makes us learn how tough our parents are可知这些表兄弟去卖菜是因为想了解父母工作是多么的辛苦,故答案为:C.
(3)A.细节理解题,根据 倒数第三段To lower the cost,they learned to bargain (讲价) with the sellers为了降低成本,他们学会了与卖家讨价还价.可知他们学会了和卖主讨价还价是为了降低成本,故答案为:A.
(4)D.标题归纳题,根据文章内容和第二段Twelve students in a big city sold vegetables at a local market together可知本文讲述的是几个表兄弟在暑假去卖菜的故事,故答案为:D