阅读理解
Every city, in fact, can be felt by its warmth-not in terms of its natural climate but its human touch.
About twenty years ago, I arrived in Australia. Searching for a place in a map in the street, I was approached by an elderly man who asked “How are you? Are you lost? How can I help you?”, which really impressed and warmed me. Another time, as I was pushing my bike on the sidewalk one night, a young lady shouted to me: “Carry me please” and then jumped onto my bicycle. While we had a little chat, she got where she wanted and hopped off my bike with “Thanks, bye!” At that moment, I had a sense as much of pleasant surprise as of “being trusted”.
Still in Australia, two of my friends decided to hitch（搭便车）their way to Sydney in order to save money. A young driver stopped, and luckily he was also going to Sydney, so he let them in and even allowed them to drive while he went to sleep on the back seat. About eight hours later, they arrived and he woke up. Saying thanks to each other, they went their separate ways.
In my opinion, no matter how developed and advanced it is, if in general a place presents itself with a cold and indifferent（冷漠的）face to people, especially to strangers, even keeping them highly alert（警惕的）not to be cheated all the time, can perhaps hardly be classified as a land of civilization（文明）. In a sense, the attitude towards strangers that the people have in the city mirrors its warmth.
的高温电离气体，气体以速度v向右流动，并通过专用管道导出。由于运动的电离气体，受到磁场的作用，将产生大小不变的电动势。若不计气体流动时的阻力，由以上条件可推导出可变电阻消耗的电功率
。调节可变电阻的阻值，根据上面的公式或你所学过的物理知识，可求得可变电阻R消耗电功率的最大值为