《钢轨探伤管理规则》规定，正线、到发线线路和道岔钢轨探伤周期当年通过总重为小于8Mt，43kg/m及以下钢轨年探伤遍数为7遍。
参考答案：对
中包保护浇注的优点？
A neutral equilibrim position for a vessel means that the metacenter is（）.
A.lower than the keel
B.at the same height as the center of gravity
C.exactly at midships
D.at the center of the waterplane area
