铜仁市对城区主干道进行绿化，计划把某一段公路的一侧全部栽上桂花树，要求路的两端各栽一棵，并且每两棵树的间隔相等。如果每隔5米栽1棵，则树苗缺21棵；如果每隔6米栽1棵，则树苗正好用完。设原有树苗x棵，则根据题意列出方程正确的是（　　）

把单位“1“分成3份，其中的2份就是 $\frac{2}{3}$ 。

    A boy lost his arms in an accident and his father lost his life. Since then, he had to1the arms of his younger brother. Except for writing with his toes(脚趾头), he could hardly do  2in his life.
    As the two brothers grew up together, they had lots of 3 and they often argued(争吵). Then one day, his younger brother 4 him. So he was very sad and didn't know 5 to do.
    A girl lost her hands because of a fire. Though her elder sister wanted to 6 her, she decided to be completely independent (独立的). At school, she always studied hard. Once she wrote the following in her composition, “I am 7. Though I lost my hands, I still have legs. Though my wings are broken, my heart can still fly.”
    One day, the boy and the girl were both invited 8 a television interview program. They both were asked to write something on a piece of paper with their toes. The boy wrote “My younger brother's arms are my arms”9 the girl wrote "Broken wings, 10 heart”.

把肯定句改成双重否定句

①教室里一阵笑声。 ②我想得是那样痴迷。