是在看足球比赛时他们扯大嗓门不停叫喊的吗？

读下面的材料和示意图，完成下列要求

材料：2014年12月26日，随着兰州到乌鲁木齐高速列车的开通，西安到乌鲁木齐已经全程告诉，兰新铁路是世界上一次性建设里程最长、我国首条在高海拔地区修建的高速铁路，全长1776公里。

①半径为 $2$ ，圆心角的弧度数为 $\frac{1}{2}$ 的扇形面积为 $\frac{1}{2}$ ；

②若 $\alpha ,\beta$ 为锐角， $\tan \left(\alpha +\beta \right)=\frac{1}{2}$ ， $\tan \beta =\frac{1}{3}$ ，则 $\alpha +2\beta =\frac{\text{π}}{4}$ 或 $\frac{5\text{π}}{4}$ ；

③函数 $y=\cos \left(2x-\frac{\text{π}}{3}\right)$ 图象的一条对称轴是 $x=\frac{2\text{π}}{3}$ .

其中真命题是____．

用科学记数法表示0.000210，结果是（    ）

    Hunting with birds is a very old sport. In some countries the golden eagles are used for hunting wild animals. They are used for hunting foxes and wolves.

    Training an eagle to hunt takes a long time. Hunters catch young eagles by using nets made of hair. After being trained, the eagle is taken to a field. A blindfold (眼罩) over the bird's eyes keeps it quiet until the hunter is ready.

    The eagle sits on the arm of me hunter. The hunter's arm is covered with a long, special glove to protect it from me sharp claws (爪子) of the bird. In the field, as soon as the hunter sees a fox or a wolf, he takes the blindfold off the eagle's eyes. The eagle quickly flies into the air and begins to look for the wild animal.

    The eagle sees the animal and catches it with claws like steel (钢铁). Its mouth and claws are strong enough to hold the animal. Usually, the bird carries the animal back to the hunter. Sometimes fast animals with good eyes can get away.