题干

如图,有一块边长为6cm的正三角形纸板,在它的三个角处分别截去一个彼此全等的筝形,再沿图中的虚线折起,做成一个无盖的直三棱柱纸盒,则该纸盒侧面积的最大值是(  )


A:3cm2

B:323cm2

C:923cm2

D:2723cm2

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答案(点此获取答案解析)

C

同类题1

阅读理解

    A company says it has completed the first 3D-printed home recently. The home was shown to reporters and visitors at a music festival.

    The building company has developed large 3D- printers that build homes with mortar, a hard and strong material. It uses robotics, computer programs and advanced materials to make houses.

    Jason Ballard is the company's chief engineer. "So I'm standing in front of the first 3D-printed home in America. This house was actually printed in high winds, blowing dust and rain." It is important for the printing programmes to operate in bad weather conditions, such as weather disasters. The goal is to print homes in developing countries. So the printer has to be light enough to move from one property to the next.

    Ballard imagines that someday, many 3D-printers will operate around the world to make homes. "It's actually a lot more simple to build a printer than it is to build a house," he said. "We ran this printer at about a quarter speed to print this house, and completed it in about 48 hours of print time."

    The company developed this technology not to make money but to help provide a quick, cheap housing solution for the millions of people who need it most. There are about a billion people that don't have one of life's most basic human needs, and that's safe shelter.

    Ballard says his company already works on housing needs with poor families in different areas. But he says that to really make a difference, the program will need to be greatly improved. He added that since the 3D-printing process is so much faster than traditional homebuilding, a whole community could be built in just a few months. He believes over time, people can get the new home below $4,000 with the help of 3D-printers.

同类题3

阅读理解

    Homestay provides English language students the opportunity to speak English outside the classroom and the experience of being part of a British home.

    What to Expect

    The host will provide accommodation and meals. Rooms will be cleaned and bedcovers changed at least once a week. You will be given the house key and the host is there to offer help and advice as well as to take an interest in your physical and mental health.

    Accommodation Zones

    Homestays are located in London mainly in Zones 2, 3 and 4 of the transport system. Most hosts do not live in the town center as much of central London is commercial and not residential. Zones 3 and 4 often offer larger accommodation in a less crowded area. It is very convenient to travel in London by underground.

Meal Plans Available

*Continental Breakfast

*Breakfast and Dinner

*Breakfast Packed Lunch and Dinner

    It's important to note that few English families still provide a traditional cooked breakfast. Your accommodation includes Continental Breakfast which normally consists of fruit juice, cereal, bread and tea or coffee. Cheese, fruit and cold meat are not normally part of a Continental Breakfast in England. Dinners usually consist of meat or fish with vegetables followed by dessert, fruit and coffee.

Friends

    If you wish to invite a friend over to visit, you must first ask your host's permission. You have no right to entertain friends in a family home as some families feel it is an invasion(侵犯) of their privacy.

    Self Catering Accommodation in Private Homes

    Accommodation on a room-only basis includes shared kitchen and bathroom facilities (设施) and often a main living room. This kind of accommodation offers an independent lifestyle and is more suitable for the long-stay student. However, it does not provide the same family atmosphere as an ordinary homestay and may not benefit those who need to practice English at home quite as much.