电路如图所示,若 u i 一定,当可变电阻 R P 的电阻值由小适当增大时,则输出电压的变化情况为 ( ) 。
A. 由小变大 B. 由大变小 C. 基本不变 D.
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On the morning of April 15, 38,500 worshippers from all over the world will descend upon the tiny town of Hopkinton, Massachusetts. In a bizarre rite they will shed most of their clothes, spread petroleum jelly over the more sensitive parts of their bodies and affix little time-keepers to their shoelaces. Then, as the appointed hour of noon approaches, they will either stand in line at one of the 750 portable toilets or, much to the chagrin of Hopkinton"s 10,000 regular residents, go natural. At the report from a gun, they will try to race 26 miles, 385 yards, all the way to Boston. In other words, they will "run Boston". And not just any "Boston". This will be the 100th Boston Marathon. The sign in Hopkinton Green that commemorates the marathon reads WELCOME TO HOPKINTON. IT ALL STARTS HERE. Actually, it all started down the road in Ashland on Patriots" Day April 19,1897, when 15 men from the Boston area and New York City entered the first Boston Athletic Association Marathon. A 22-year-old lithographer from New York named John McDermott won the race, though not easily. A few miles from the finish McDermott had to stop because of intense leg cramps. Fortunately, he had an attendant who answered McDermott"s command, "Rub!" and he crossed the finish line in 2:55:10—which would have been good enough for683rd place in last year"s Boston Marathon. Times have changed, of course. The road to Boston is now paved. The leather shoes that McDermott wore gave way to canvas sneakers that gave way to leather shoes. The start was moved from Ashland to Hopkinton in 1924 in order to lengthen the course to the classic marathon distance. And in recent years, the traditional post-marathon beef stew served by the BAA has been replaced by a pre-marathon pasta party sponsored by Ronzoni. But from the beginning, Boston has been immensely popular: the seventh running of the marathon in 1903 attracted 200,000 spectators. This year an estimated 1.5 million will cheer the runners on as they move from Hopkinton to Ashland to Framingham to Natick to Wellesley to... "Its obvious strength is 100 years of the best runners in the world," says Bill Rodgers, the folk hero who has won Boston four times. "But it is also the best course anywhere. You run through small towns on your way to Boston. You really have a sense of making progress." If Boston has a patron saint, it is John A. Kelley, who first ran the race in 1928 when he was 20 and last ran the race in 1992 when ha was 84. In 1935 Kelley, who was then a floral assistant outdueled toolmaker Pat Dengis, eliciting this response from Dengis: "Would you imagine this, a florist runs 26 miles for a laurel wreath!" Though he received a police escort home to Arlington, Massachusetts, and a telegram from the Governor, Kelley was back at work the next day, preparing Easter lilies at Anderson"s Florist Shop. He also won in 1945 at the advanced age of 37 and told a reporter, "Life merely begins at 40, and I have three years to go." Kelley no longer runs in the marathon, but runners can still pass him on Heartbreak Hill in Newton, where there are twin statues of Kelley—as he ran in his first victory and as he ran in his 61st Boston.
A．The leather shoes have given way to canvas sneakers.B．The course of the marathon has been completely changed.C．The traditional post-marathon beef stew is now served by Ronzoni instead of BAA.D．The starting point has changed from Ashland to Hopkinton.
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