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举一反三
【单选题】第二篇 Pushbike Peril Low speed bicycle crashes can badly injure—or even kill—children if they fall onto the ends of the handlebars (车把). So a team of engineers is redesigning the humble h...
A.
it is not easy to persuade manufacturers to adopt the new design.
B.
the team of engineers has not found any countermeasures.
C.
children like to ride bicycles at a very low speed.
D.
a lot of children were killed in bicycle accidents in the past 30 years.
【单选题】(2005年)要用冲床在厚度为t的钢板上冲出一圆孔，则冲力大小( )。
A.
与圆孔直径的平方成正比
B.
与圆孔直径的平方根成正比
C.
与圆孔直径成正比
D.
与圆孔直径的三次方成正比