问题 选择题

某精密电子仪器中为了便于调节电路中的电流,其调节部分使用了两个滑动变阻器,如图所示。已知这两个滑动变阻器是分别用不同的电阻丝绕在相同的绝缘瓷管上制成的,其中R1的总电阻是200Ω,R2的总电阻5000Ω,开始时两变阻器都处于最大阻值。下面的几种方法中,能够既快又准确地使电流表指针指到要求位置的是

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A. 先调节R1,使电流表指针指到要求位置附近,再调节R2

B. 先调节R2,使电流表指针指到要求位置附近,再调节R1

C. 同时调节R1和R2,使电流表指针指到要求位置

D. 交替、反复调节R3和R2,使电流表指针指到要求位置

答案

B

阅读理解

LOS ANGELES--- Two lost hikers who survived three nights in mountains thanks to supplies at a campsite of another hiker who disappeared last year described their suffering, saying they had “the real special thank” for the man who is probably dead.

The couple, Allen, 24, and Brandon Day, 28, were in Southern California for an important conference. They got lost on Saturday west of Palm Springs after wandering off a trail during what was supposed to be a day hike.

Prepared only for a brief hike, they wore light jackets and tennis shoes and had no food, spare clothing or mobile phone. With night closing in, they took shelter in a small cave and spent the night sleepless, freezing and hungry.

On Monday, they discovered a campsite in a dead valley. There was a sleeping mat, a backpack, a disposable razor(一次性剃刀), a spoon and tennis shoes. Day and Allen were delighted, thinking someone there could help them find the way out. But later they realized the place was deserted.

They found identification showing the camper was Donovan, 60, a retired social worker from Virginia. They learned later in his diary that he was an experienced hiker and he disappeared on May 2, 2005, in icy weather.

They found articles in his backpack: a warm sweater for Allen, dry socks for Day and matches. They lit a small signal fire to attract a helicopter crew in the distance, but the crew did not see them.

On Tuesday morning, Day created “a really big smoke signal” that finally attracted a helicopter crew. They were examined at a hospital and had only bruises(擦伤).

“We feel great. We’re thankful. We feel like we’ve been given a second chance,” said Day, who expressed that they wouldn’t give up hiking even after this experience.

1. The passage most probably appears in ________.

A. an advertisement             B. a newspaper    C. a travel guidebook        D. a travel journal

2. Why did Allen and Day go to Southern California?

A. To go for a short hiking in mountains.    B. To search for the hiker missing a year ago.

C. To attend an important conference.      D. To enjoy the scenery of Palm Springs.

3. Which of the things the couple found helped them the most?

A. Tennis shoes.      B. A sleeping mat.        C. a warm sweater.     D. Matches.

4. Which of the following statements is TURE?

A. The couple realized the campsite was deserted the moment they found it.

B. The couple at first thought the person in the camp could help them out.

C. It was the icy weather that led to Donovan’s disappearance and death.

D. This experience would prevent the couple hiking again in future.

填空题