飞机的发动机是一种热机，通过航空煤油在气室中燃烧，从喷口向后高速喷出气体，使发动机获得向前的推力，高空中某飞机获得1.6×10⁵N的水平推力，以600km/h的速度沿水平方向匀速航行1h，需要完全燃烧热值为4×10⁷J/kg的航空煤油4000kg．求1h内：

常见的晶体有如下类型：①分子晶体  ②离子晶体   ③原子晶体 ④金属晶体，由非金属元素所形成的单质或化合物中，固态时的晶体类型可以是（    ）

阅读下面材料, 在空白处填入适当内容 (一个单词）或括号内单词的适当形式。讲答案填写在答题纸的相应位置。
       What's the most important thing for you to have in your life? Somebody ____ (mention)hard-work, others suggest knowledge, love and luck.
       If you arrange the 26 English letters alphabetically(按字母表的顺序)and use ____(number)to represent each of them, for example, 1 for a, 2 for b, 3 for c…, you can change an English word into a number. So hard-work becomes 8+1+18+4+23+15+18+11=98, meaning 98 is its mark; knowledge: 11+14+15+23+12+5+4+7+5=96, while love :12+15+22+5=54, and luck : 12+21+3+11=47, a small mark. None of these words can give one a full mark. What about money or prayer(祈祷)? They can't , ____.
       Then what else? Don't be worried. You can always find an answer ____a problem in your life, ____you change your way of looking at things or doing things, or your attitude. Yes, attitude is the word. See for____(you): attitude:1+20+20+9+20+21+4+5=100, a full mark.
       Different attitudes lead to different courses of life. Most times people hope for a better life. It is possible ____one will have a change for the better after one has ____(change)one's attitude.
       When you change your manner and became friendly towards others, you'll meet ____ (much)smiling faces towards you. In the same way, if you take a positive attitude towards failure, you'll find it's also rewarding ____it has caused you losses.

双曲线 $\frac{x^2}{a^2}-\frac{y^2}{b^2}=1\left(a>0,b>0\right)$ 的渐近线为等边三角形OAB的边OA，OB所在直线，直线AB过双曲线的焦点，且|AB|=2，则a=____．

根据短文阅读，选择正确答案。

    I'm Mary. This is my friend. Polly. Look! It is yellow and brown. It's fat. Its ears are small. Its eyes are big. Its tail is long. Polly likes fish and milk. It doesn't like fruit. Polly can hop and run. But it can't swim. It likes playing with a ball. I usually go to the park at the weekend(周末). Polly follows(跟随)me. I fly my kite in the park. Polly runs after me. What is Polly? Do you know? It's a cat.