默写填空  

所有的原核细胞都具有:

若函数f（x）= $\{\begin{array}{c}sin\left(2x-\frac{\pi }{6}\right)，-\pi \le x<m\\ cos\left(2x-\frac{\pi }{6}\right)，m\le x\le \frac{\pi }{2}\end{array}$ 恰有4个零点，则m的取值范围为（　　）

已知；（NH₄）₂CO₃（s）═NH₄HCO₃（s）+NH₃（g）△H=+74.9kJ•mol^﹣1，下列说法中正确的是（  ）

根据短文内容，选择正确答案。
A
    One day, Mr. and Mrs. White went shopping by car. They stopped their car near a store. They bought a lot of things and they wanted to put them in their car. But Mr. White couldn't open the door of the car. “Let's ask a policeman for help.” said Mrs. White. They asked a policeman to help them. The policeman was very friendly to help them open the door of the car. Just then a man came up and shouted, “What are you doing with my car?” Mr. and Mrs. White took a look at the number of the car. It was not their car.