题干

在等高线地形图上,下列叙述正确的是(    )

A:等高线向高处凸出时则为山谷

B:等高线向低处凸出时则为山谷

C:等高线呈闭合的地区,表示的是山地

D:同一条等高线海拔高度不等

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答案(点此获取答案解析)

A

同类题3

完形填空

    On July 24, 1916, a natural gas explosion trapped 32 men working in a tunnel 250 feet below Lake Erie. The first rescuers who entered the tunnel were 1 by gas, and for hours no one else dared to enter the suffocating (窒息的)2 deathtrap.

    Then, late that night, someone had an idea3 Garrett Morgan and his new invention. Garrett Morgan was a successful 4 owner in Cleveland. The son of freed slaves and the seventh of 11 children, mechanically minded Morgan had opened his own sewing machine shop, which he soon 5 to a tailoring factory with 32 employees.

    In the early 1900s, factory buildings were crowded and untidy. They were often6 of wood, with no fire escapes. Fire could cause serious7 Concerned about his employees, Morgan 8 with a “safety hood” (头罩) that would allow the wearer to9 despite a fire's poisonous smoke.

    Morgan knew smoke rises during a fire10 he created a heat-resistant hood with a long tube reaching to the floor. Wearing Morgan's hood, a firefighter could breathe the 11 air near the 12 Morgan lined the breathing tube with a sponge-like material that was wetted before use to13 the air. A second tube was designed to14 exhaled (呼出的) air.

    Called to the scene on the night of the tunnel explosion, Garrett arrived with samples of his safety hood. Still in their nightwear, he and his brother Frank put on the hoods and 15 entered the tunnel. It was a dangerous 16 of the invention, but they saved two lives and 17four bodies before officials closed the18Morgan knew that more lives might have been saved if he had been called sooner.

    The daring19 made Morgan famous and brought requests for safety hoods from fire departments around the country. But his greatest20 was knowing that his invention would now save more people.