题干

有关下列说法中,完全正确的组合是      
①将某精原细胞的DNA用15N标记后将该细胞转入含14N的培养基中培养,若进行减数分裂形成四个精子,则其中所有的DNA均含有15N ②受精卵中的遗传物质一半来自父方,一半来自母方 ③用基因型为DdTt的植株进行单倍体育种,所育的种自交后代约有1/16为纯合子 ④细菌分裂生殖时,导致子代之间差异的可能原因是基因突变和染色体变异 ⑤若女孩是色盲基因携带者,则该色盲基因可能来自其父亲

A:①②④⑤

B:②③④⑤

C:①③⑤

D:①⑤

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D

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    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.