氧化钙，俗称生石灰，是灰泥中的主要成分之一。灰泥被称为建筑用“胶”，它能将墙砖粘合在一起，密度为2.2×10³kg/m³。请写出泥灰从与水混合到粘合好墙砖的整个过程中的其中一个化学反应方程式____。若每块砖的厚度是7 cm，密度为2.4×10³ kg/m³，设砖缝间建筑用胶的厚度为1cm。为了保证安全，墙体对墙基的压强不得超过4.9×10⁵Pa，那么，该墙的高度不得超过____m。（不考虑大气压强，计算结果保留两位小数）

阅读理解

A

    Nick, 13, is tall and strong. He is good at running. Two weeks ago a new student came. His name is David. He is thin and short. He plays soccer well, and he can run very fast. Larry told Nick about it. Of course, Nick did not believe it.

    “Why not have a race with him?” said Larry.

    “Good idea!” said Nick. “I'll have a race with him after school.”

    After school, Nick went to the playground. He did some warm-up exercises for half an hour, and got ready for the race. He was sure that he could win it. Larry had to take part in a club activity that afternoon, so he could not watch the race between Nick and David.

    That evening Larry went to see Nick. They began to talk about the afternoon race. Nick's grandmother heard them in the next room. She came in and asked, “Which place?”

    “The second place,” answered Nick.

    His grandmother was very happy to hear that, and asked, “Which place did David win, then?”

    “The last but one.”

丽丽用4米长的竹竿量井深，竹竿露出井沿部分是1米．井深____米.

已知随机变量服从正态分布，,则（    ）

某食品袋中有一个写着“干燥剂”的小纸袋，里面的主要成分是生石灰，对此“干燥剂”的说法正确的是（   ）