题目:
For any piston ring to operate smoothly without scuffing ,the ring must be ().
A.of a material harder than the cylinder liner
B.properly lubricated
C.prevented from compressing
D.prevented from rotating during engine operation
答案:
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参考答案:C解析:该题是基本概念题,备选答案是眼科常用的影像学检查。MRI是利用人体内的氢原子中的质子在强磁场内被相适应频率的射频脉冲激发,质子吸收能量产生共振。射频脉冲终止后质子恢复原态时释放出能量...