已知平面向量$\overrightarrow{a}=\left(2,1\right),\overrightarrow{b}=\left(x,-2\right)$，且$\overrightarrow{a}\perp \overrightarrow{b}$，则x=  （    ）

小红同学对串联电路电压规律进行了探究

【猜想与假设】串联电路总电压等于各用电器两端的电压之和

【设计与进行实验】

（1）按如图所示电路图连接电路．

（2）闭合开关，排除故障，用电压表测出L₁两端的电压．

（3）在测L₂两端的电压时，小明为了节省时间，采用以下方法：电压表所接的B接点不动，只断开A接点，并改接到C接点上．

（4）测出AC间的电压，得出结论．

【交流与评估】

阅读理解

Why I've taken a break from holidays

    It is now close to four years since I last took a holiday. This is because I have come to the conclusion, over the course of my adult life, that I am not very good at it. You might think this sounds like saying you're not very good at drinking tea or listening to music. What could possibly be difficult about the natural act of putting your working life on hold for a couple of weeks and going somewhere warm to do nothing?

    I was a model holidaymaker as a kid. However, the problems started during my twenties. A trip to the south of France was ended after just two days, mainly because I had an urge to check my e-mails. Similarly, my honeymoon was cut short by 48 hours—not because my wife and I weren't enjoying ourselves, but because we were missing our cats.

    So what is my problem? On the surface, I'm probably a bit of a homebody. And I just find the pressure of being on holiday too severe: it always feels like having a gun held to my head and being forced to have fun. Somehow, packing a list of possessions and meeting a scheduled flight has none of the excitement of suddenly deciding to take a day off and driving somewhere for the fun of it.

    Thankfully, I'm not alone. This summer, most of my friends have decided not to have a break. And a recent survey (调查) proved the downside of holidays, with the results showing that nearly two thirds of people found that the calming effects of a holiday wore off within 24 hours, as stress levels returned to normal. And this year The Idler magazine published its Book of Awful Holidays. Here you will find a list of the five most ecologically-damaging vacations it's possible to take, along with 50 painful holiday experiences voted for on The Idler website.

    What interests me is what the concept of a “holiday” says about our lives. For me, the point of living is to have a life you enjoy for 52 weeks a year. The more I like my life and the better I structure it, the less I want to go away. Maybe I'm an unusual person for not liking holidays, but I just feel the time when I'm not working is too valuable to waste on them.

阅读下面这首诗，完成下列问题。

长相思^①

李白

长相思，在长安。

络纬^②秋啼金井阑^③，微霜凄凄簟色寒。

孤灯不明思欲绝，卷帷望月空长叹。

美人如花隔云端。

上有青冥之高天，下有渌水之波澜。

天长路远魂飞苦，梦魂不到关山难。

长相思，摧心肝。

注：①有人说，此诗写于作者遭权贵排挤，离开长安后。②络纬：纺织娘，虫名。③金井阑：有雕栏的井，在古诗文中用来美称宫廷或园林中的井。