E Erica David lives in Pinedale,Wyoming，USA，where winter can bring temperatures of below 35 degrees Fahrenheit，howling winds，and a lot of snow．So it was just natural that she chose to study snow for her school science fair in the sixth grade． Now a junior in high school，Erica is in her sixth year of snow experiments，and is well on her way to becoming a snow expert．She started with a basic question：Could snow fences be built to work better? Snow fences are used to keep snowdrifts（雪堆）from covering areas like roads of train tracks，or to help build up snow where it can help with water shortages in spring when it melts（融化）．“Also，I wanted to protect my animals better from blowing snow，”says Erica，who raises goats，sheep，and pigs． Before she could test fence designs，Erica had to figure out what would act like real snow in her experiments. “I tested flour, sugar, and salt before I settled on dishwasher powder , ”she explains. Science fairs offer students the chance to test theories, present findings to judges, and meet other researchers. Erica’s many achievements include competing at the Discovery Channel Young Scientist Challenge for middle school students and the Intel International Science and Engineering Fair, where students from around the world present their science research. But perhaps the best reward is that her research is already being put to good use. She has come up with an improved snow fence design, and this year she’s helping think out how to provide water supply to native plants, which have been killed off by drilling at nearby natural gasfields. “Science fairs are an amazing experience,”says Erica. “Just pick your true feeling and go for it. ” 72. What does the passage suggest to us? A. Science fairs are held for high school students in America. B. Erica is the youngest show expert well known in America. C. The environment brought much convenience for Erica to study snow. D. The hope to contribute to her hometown made Erica experiment on snow. 73. In Erica’s hometown, snow fences may play a part in ________. a. reducing the harm blowing snow does to animals b. supplying water resource to the nearby gas fields c. up for the lack of water resource. d. keeping the traffic smooth A. a,b,c          B. a,b,d             C. b,c,d            D. a,c,d 74. Science fairs are attractive to students because they ________. A. can have their research put into practical use B. can have their scientific ideas tested out C. are allowed to help protect the local wildlife D. can learn about the most advanced technology 75. Which of the following material can best replace snowing in Erica’s experiment? A. Flour.         B. Sugar.           C. Salt.             D. Dishwasher powder.