单项选择题

下列数据模型中，具有坚实理论基础的是（）。

A.层次模型
B.网状模型
C.关系模型
D.以上3个都是

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单项选择题

开发软件所需高成本和产品的低质量之间有着尖锐的矛盾，这种现象称为（）

A.软件投机
B.软件危机
C.软件工程
D.软件产生

单项选择题

听力原文： For years now, the world's fastest trains, operating in Japan and France, .have been stuck at a maximum operating speed of around three hundred kilometers an hour--in fact the latest Japanese bullet trains travel a bit slower than their predecessors, the emphasis of the designers being more on smoothness and economy. Now JR East, the country's largest railway company, has unveiled a much faster train, capable of sustained speeds of around 360 kilometers an hour. The new train, which has been displayed in a dazzling teal color, looks very similar to the streamlined models already running on Japan's high-speed railways, except for one unusual feature--extra emergency brakes in the form. of cat's ears--this, a response to the derailment of a bullet train after an earthquake last year.The Japanese bullet trains ______ .A．can run faster than 300 kilometers an hourB．run more smoothlyC．are more costlyD．are much more beautiful

A.have
B.
C.
The
D.
A．can
E.run
F.are
G.are

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