预防煤炭自然火灾主要有四个方面的措施，即：开拓开采技术措施、（）措施、（）措施和预防性灌浆措施。
参考答案：防止漏风；阻化剂防火
单位重量粉粒所具有的表面积称为（）。
Which conditions will normally cause a SART to operate in the active mode?（）
A.It will respond only to interrogation by 9-Ghz radar signals
B.A SART will normally respond to interrogation from a searching vessel's radar if the radar antenna is at least 15 meters high
C.A SART will normally respond to interrogation from a searching aircraft's radar if the radar's output power is at least 10，000 watts and the aircraft is at a height of 3000 feet and within 30 nautical miles
D.All of the above
