题干

某同学在做“调节灯泡亮度”的电学实验时,电路如图所示,电源电压恒为6V,电流表的量程为“0~0.6A”,电压表量程“0~3V”,滑动变阻器的规格为“20Ω 2A”,灯泡L标有“3V 0.9W”字样(忽略灯丝电阻变化).在实验中为了保证所有元件的安全,下列判断正确的是(   )

A:该电路中,变阻器R接入电路的阻值变化范围为0~20Ω

B:该电路消耗的总功率的变化范围为1.2W~3.6W

C:该电路中,电流表示数的变化范围为0.2A~0.6A

D:该电路中,电灯消耗功率的变化范围为0.4W~0.9W

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D

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    For the first time in the history of the Beijing, Shanghai and Hangzhou marathons, fourteen blind runners competed in the Nov 6 Hangzhou Marathon this year with the assistance of personal guides. Each runner was supported by 4 or 5 volunteers. Among them was Yan Wei, from a running group called “Running in the Dark”, which specially provides training for blind runners.

    During trainings, blind runners are each accompanied by three volunteers. One volunteer is responsible for removing any obstacles(障碍物)on the road and controlling the pace. The second volunteer acts as a lookout for other runners or vehicles on the path while the third, who is attached to the blind runner by a safety rope, takes note of the trainee's running gait and pace.

    Zhu Peihua, the leader of the group's Shanghai branch, first developed a passion for running last year when he took part in a guided running activity. Zhu said that he was so fascinated with the sport that he even bought a treadmill(跑步机)so that he could train at home. “Running gives me the chance to be outside and take in the fresh air. The activity has also made me more willing to talk to people. It's simply good for health, ” said Zhu.

    The popularity of guided running activities for blind people has been growing since last year. Cheng Yi, a volunteer at Running in the Dark's Hangzhou branch, said that both the numbers of blind runners and volunteers to become assistants to them are rising continually. However, he added that volunteers face a more physically demanding task compared to a regular runner. Some of the other challenges involve being aware of the verbal(口头的) instructions one gives.

     “At the beginning, I kept saying ‘here' and ‘there' instead of ‘left' or 'right' which is much more specific and relevant to the runner. A blind runner once collided with another runner because of my mistake. Luckily, no one was hurt,” said Cheng. Through everything, according to Cheng, he and many of the blind runners he has guided become close friends with shared topics and increased understandings.