锅炉满水事故可能会造成（）
A.蒸汽管道产生水击
B.蒸汽大量带水
C.过热蒸汽温度急剧上升
D.过热器内积垢
参考答案：A, B, D
It is said that the early European playing-cards ______ for entertainment and education.[ ]
A. were designed
B. have designed
C. have been designed
D. were being designed
开展教育实践活动应遵循哪些原则？
