题干

下列问题的研究中,没有利用对比实验思想方法的是(  )

A:研究空气中氧气的含量

B:研究微粒的运动

C:研究木炭在氧气在燃烧

D:研究铁生锈的条件

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答案(点此获取答案解析)

A

同类题3

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    Who could have imagined that a treadmill(跑步机)on wheels would one day become a thing? Lopifit is an unusual means of transportation that allows you to power an electric bicycle by walking on a treadmill.

    Lopifit founder Bruin Bergmeester says it all started when he asked himself the question. "How can I use a treadmill outdoors?" He eventually came up with a design, to which he added an electric engine, and Lopifit was born. The treadmill bicycle is similar to a typical electric bicycle in that the motor only works when the rider puts power in as well. The Lopifit senses it when you walk on the treadmill and uses the motor to turn a drive chain at the back part of the treadmill, helping you reach a top speed of 17 miles per hour.

    To use the Lopifit, simply turn on the battery and use your feet to slide the treadmill backwards and activate (激活) the motor. Then get on and enjoy the ride! If you need speed, just walk on the treadmill, and if you want to coast, all you have to do is stay still and admire the view. To stop, you have two hand brakes available.

    The Lopifit first hit the streets in 2014 and, unsurprisingly, became an instant hit. That was actually quite challenging for the company, because it started get inquiries and calls for orders, but it was nowhere near ready for mass production. The unique treadmill bicycle became available this year, and Lopifit is struggling to keep up with demand, despite the high price tag of $ 2,115.

    But despite having a very loyal fan-base of so-called Lopifitters, the creative means of transportation also has naysayers who simply consider the invention stupid and unnecessary. They basically believe that if you're going to walk, you might as well do it the old-fashioned way. But the Lopifit does have the unique advantage of helping you walk really fast without breaking a sweat, or walking at cycling speed, if you will.

同类题4

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Jacob's Pillow Dance Festival

Where: Becket, Massachusetts

When: June 15-Aug 24

    Each summer, this influential dance center presents a number of classes and performances by more than 50 companies from around the world. Highlights (最精彩的部分) this season include the Dance Theater of Harlem's production of Alvin Ailey's “The Lark Ascending”, which opens the festival.

    Many events are free. Ticketed performances start at $22. jacobspillow.org.

Moab Music Festival

Where: Moab, Utah

When: Aug 29-Sept 9

    This area is better known for mountain biking than for music. But since 1992, it has hosted a private festival that brings classical, jazz, Latin and other types of music to the land. This year there will be 16 concerts, including three “Grotto Concerts”, where guests take a 45-minute boat ride down the Colorado River to performances.

Events start at $25. moabmusicfest.org.

Cheyenne Frontier Days

Where: Cheyenne, Wyoming

When: July 19-28

    There's something for everyone at this 117-year-old festival, from an “Indian village” and Old West museum to country concerts. But the competition is still the main attraction, with cowboys and cowgirls competing for major money in the world's largest outdoor stage.

Competition tickets start at $18, and concert tickets at $23. cfdrodeo.com.

The Glimmerglass Festival

Where: Cooperstown, New York

When: July 6-Aug 24

    Each summer, opera lovers from around the country (and the world) travel to upstate New York to watch productions that include stars like Nathan Gunn and Ginger Costa-Jackson. This year's performances include Wagner's “The Flying Dutchman” and Verdi's “King for a Day”, in honor of the 200th birthdays of both composers (作曲家).

Tickets start at $26. glimmerglass.org.