题干

实验室制取二氧化碳的最合适的原料是(   )

A:石灰石与浓盐酸

B:石灰石与稀盐酸

C:碳酸钠与稀盐酸

D:石灰石与稀硫酸

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答案(点此获取答案解析)

B

同类题1

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    I remember my childhood summers fondly, as many of us do. Those golden days in which I would leave the house after a still sleepy, leisurely breakfast and come home only for lunch in the middle of a day spent entirely outdoors. We did not live in town and, thus, playmates were limited to siblings (兄弟姐妹) and the cousins who lived down the road.

    Our backyard became the playground in which our imaginations would run wild—turning those few acres into magical forests, the creek (小溪) into a violent river and our trusty dog, Rex, into the many roles of horse, monster and any other creature that we children did not want to play. By the end of the three months of summer break we were sunburned from our hours in the sun, full of the memories of a thousand magical moments and bonded to our siblings in a way that winter's forced hibernation (冬眠) never seemed to connect us.

    Today, I live on the same acreage that I did as a child. My children have the blessing of having the same grassy patches to scratch their bare feet as they run through it, the same creek to stomp(跺脚)through, and not the same dog—but their very own energetic pup to imagine away the days with.

    However, this is not the same world as it was twenty, thirty years ago. There are screens everywhere in the house to demand attention—televisions with hundreds of channels, computers with access to a thousand entertaining sites, tablets stocked with apps. There is also no longer the expectation of a stretch of an unscheduled three months. Their school friends tell competitive stories of carefully planned vacations, spending time traveling to all of the local attractions—various parks, the zoo, the science center, all of the festivals which come breezing through town. On the very first day of school they will be asked to list their favorite activities of the summer and no longer are these lists filled with things like finding wood to make a bridge over a creek or a day spent in imaginative play with their siblings. The lists are now full of trips, overscheduled days and “camps” that no longer offer a stay in nature.

    Our children have become used to being entertained every minute. In our house, we have limits on electronics and kick the kids outside on a nice day. Even as we try as parents to set limits and get our children out in nature, the new cry of childhood seems to be “I'm bored,” which is not really just meaning “I'm bored,” “but “Please find something to entertain me, as I no longer can entertain myself even for a short period of time.” Our children no longer know how to sit in silence, entertain themselves while even waiting for a few minutes and have lost the awe of nature as they have become addicted to screen time.

    We have made a choice in this household to do what is no longer expected of children in many households—we will ensure that there are days of “boredom.” We refuse to spend our days scheduling our children's every hour. There will be many days with no plans at all, when they will be sent outside with only the grass and the trees and their own imaginations to entertain them.

    The screens will be turned off and our children will find that times of quiet can be just as or even more entertaining. They will bond with their brother and sister, making memories that they will replay in their minds well into adulthood. Even though sunscreen will be religiously applied, they will leave summer with sunburned and scratches coming from climbing trees, stomping through creeks and chasing the dog in the field.

    This summer I will be giving my children the greatest gift of all—boredom. For inside boredom is the gift of getting to know your own mind, of finding comfort and joy in nature and in the realization that the greatest gifts are experience, not things.

同类题5

阅读理解

    Golden Gate Bridge

    Located in San Francisco,the Golden Gate Bridge started in the year 1933 to connect the San Francisco Peninsula with Marin County.It was finally thrown open to public traffic in 1937.It cost $25.7 million in the construction.Till the year 1957,the Golden Gate Bridge,at a length of 2,737 meters,was the longest suspension bridge in the world.

    Brooklyn Bridge

    The Brooklyn Bridge is located in Brooklyn.It is one of the oldest suspension bridges in the United States, having been opened in the year 1883.The length of the bridge is 1,843 meters.The bridge has been featured in several Hollywood movies.

    George Washington Bridge

    Also known as the Hudson River Bridge and the Columbus Bridge,the George Washington Bridge which connects Fort Lee to Manhattan came into use in 1931 after a construction period of almost 4 years.It is a two level suspension bridge that cost about $52 million to build.

    Mackinac Bridge

    This is the third biggest suspension bridge in the world at a length of 8,038 meters.The architect of this bridge was Dr.David B. Steinman who directed the construction of the bridge which started in the year 1054 and opened to the public in 1958.People using this bridge are charged a certain amount of money.

    Navajo Bridge

    Located in Arizona,this bridge crosses the Colorado River and is almost 250 meters long.The construction of this bridge started in the year 1927,ending two years later,costing $390,000.In the 1990s a second bridge was built which was opened to the public in 1994.The first bridge is now used only by pedestrians.