第11题:[单选题]An essential traffic message should be in such a form that the traffic can be easily identified and contains the following elements: _______ . A.direction of flight B.type of an aircraft C.cruising level and estimated time over the most suitable reporting point D.all the above 参考答案:A
第12题: [单项选择]硫化氢的爆炸极限是()。 A. 5%~15% B. 3.5%~35% C. 5%~50% D. 4.3%~45.5% 参考答案:D