[单选题]《普速铁路线路修理规则》钢轨低头：用1m直尺测量最低处矢度，包括轨端轨顶面压伤和磨耗在内，υmax≤120km/h超过（ ）为重伤。
A.1.5mm
B.2.5mm
C.3.0mm
D.3.5mm

If it were only necessary to decide whether to teach elementary science to everyone on a mass basis or to find the gifted few and take them as far as they can go, our task would be fairly simple. The public school system, however, has no such choice, for the two jobs must be carried on at the same time. Because we depend so heavily upon science and technology for our progress, we must produce specialists in many fields. Because we live in a democratic nation, whose citizens make the policies for the nation, large numbers of us must be educated to understand, to support, and when necessary, to judge the work of experts. The public school must educate both producers and users of scientific services.
In education there should be a good balance among the branches of knowledge that contribute to effective thinking and wise judgement. Such balance is defeated by too much emphasis on any one field. This question of balance involves not only the relation of the natural sciences,
A. One of the major tasks of education is to discover the most promising students.
B. In order to teach effectively, educators are requested to lay emphasis on one particular field.
C. Some subjects have been over-emphasized in public schools.
D. The progress of the society can not merely rely on inventors.