第29题: [单项选择]X线胶片的感光银盐颗粒大小平均为 A. 1.71nm B. 1.71Pm C. 1.71mm D. 1.71cm E. 1.71dm 参考答案:B 答案解析:X线胶片的卤化银盐颗粒平均为1.71μm,在感光材料中是最大的。
第30题: [单项选择]Upon completion of fueling a gasoline driven vessel it is necessary to(). A. keep ports,doors,windows,and hatches closed B. start engines immediately C. ventilate before starting engine D. None of the above 参考答案:C