把肯定句改成双重否定句
①他见义勇为的行为，让我们深受感动。
②我们建成了希望小学。
①他见义勇为的行为，我们不能不深受感动。
②我们不是没有建成了希望小学。
A
It's a beautiful day in summer. There are many people on the beach. Mrs Guo and her two sons are on the beach, too. Look! Mrs Guo is swimming in the sea. She can swim fast. What are her sons doing? They are playing volleyball on the beach. There's a man under the umbrella. He's reading a book. Look! A little girl is collecting shells on the beach. She's very happy.
俄罗斯大河很多，除伏尔加河外航运价值不大，最重要的原因是（ ）
材料一：江南地广人稀……火耕而水耨（用烧荒和原始的水稻耕作技术从事农业生产）……无冻饿之人，亦无千金之家。
——《史记》
材料二：江南……民勤本业……丝绵布帛之饶，覆衣天下。
——《宋书》
材料三：东晋南迁移民分布图
回答问题：
已知点P(x,y)在经过A3,0,B1,1两点的直线上，则2x+4y的最小值为( )
