【C14】______ in recent years plastics have replaced glass 【C15】______ conditions where glass might be 【C16】______ broken there are new uses 【C17】______ for glass that were never imagined in the 【C18】______ . Perhaps the greatest 【C19】______ . of glass is that its constituent (形成的) parts are inexpensive and can be found 【C20】______ over the world.
【C1】_____
A.they
B.do they
C.they have
D.have they
第3题
A.周围和空间必须有可燃物存在
B.具有产生和累积静电的条件
C.静电累积到足够高的静电电位,可将周围的空气介质击穿而产生放电,构成放电的条件
D.静电放电的能量,大于或等于可燃物的最小点火能量
E.发生在爆炸性环境中
第5题
(A)短路
(B)接触不良
(C)过载
(D)静电
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