用同一列有轨机车送炸药和雷管时，必须将雷管与装炸药分别放在两个车辆内。()
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下列除哪项外均为大气污染对健康的直接损害
A. 急性中毒
B. 机体免疫力下降
C. 致癌作用
D. 变态反应
E. 儿童维生素D缺乏病的发生增加
Manufacturers oppose retailers cutting prices on their goods mainly because they think_____.
A. retailers may eventually stop selling their products
B. it may reduce customers"confidence in their products
C. customers may feel uneasy when prices vary
D. it may sometimes lead to poor service
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