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A pilot cannot fly a plane by sight alone. In many conditions, such as flying at night and landing in dense fog, a pilot must use radar, an alternative way of navigating. Since human eyes are not very good at determining speeds of approaching objects, radar can show a pilot how fast nearby planes are moving. The basic principle of radar is exemplified by what happens when one shouts in a cave. The echo of the sounds against the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of sound waves. Radio waves travel at the speed of light, about 300, 000 kilometers in one second. A radar set sends out a short burst of radio waves: Then it receives the echoes produced when the waves bounce off objects. By determining the time it takes for the echoes to return to the radar set, a trained technici A. Argumentative. B. Imaginative. C. Explanatory. D. Humorous. [单选题]左心衰竭患者的呼吸困难主要是由于
A.肺瘀血或肺水肿所致 B.肺泡内张力和肺循环压力增高所致 C.体循环瘀血所致 D.肝瘀血、腹水等使呼吸运动受限所致 E.支气管、肺受压所致 [单项选择]Some people oppose the ownership of H-bombs by individuals on the grounds that ______
[判断题]装卸易燃、易爆货物时,工属具应降低额定负荷量的 5%使用。( )
A.正确 B.错误 [单选题]光卤石原矿K+≥ ( )
A. 6.8% B.3.0% C.5.0% D.6.0% [多选题]动车组车下电源包括哪几部分( )。
A.2×35kVA逆变器 B.8KW充电机 C.3.5KVA单项逆变器 D.15kW隔离变压器 [单项选择]平静呼吸时肺通气的阻力主要是（）
A. 胸廓的弹性回缩力 B. 气体进出气道时产生的摩擦阻力 C. 胸廓的惯性阻力 D. 肺的弹性回缩力 E. 肺组织移位的惯性阻力 [单选题]根据《东京公约》的规定，缔约国接受机长移交并采取拘留措施后，以下说法正确的是（ ）。
A.可允许行为人联系其本国最近的合格代表 B.不可允许行为人联系其本国最近的合格代表 C.行为人联系其本国代表时可以予以协助 D.行为人联系其本国代表时无需予以协助 [单项选择]慢性肾功能不全，血钾7.1mmol/L时，此时最佳的治疗措施是（）
A. 限制钾盐的摄入 B. 口服降钾树脂 C. 静推10%葡萄糖酸钙 D. 静注碳酸氢钠 E. 血液透析或腹膜透析 [单选题]CRH380B（L）安装新闸片，作业人员用双手托住新闸片底部和侧面，将闸片放到闸片托架的（ ）中并沿弧形缓慢送入闸片托内。
A.槽 B.支架 C.止铁 D.导轨 [单项选择]对青霉素G最敏感的病原体是( )
A. 立克次体 B. 钩端螺旋体 C. 衣原体 D. 支原体 E. 真菌 [单选题]根据《安全生产许可证条例》的规定,安全生产许可证的有效期为( )年。
A.1. B.2. C.3. D.4. [单选题]急性阑尾炎，当腹痛尚未转移至右下腹前，最具诊断意义的是
A.A:发热 B.B:白细胞升高 C.C:脐区压痛及反跳痛 D.D:脐区及右下腹均有压痛、反跳痛 E.E:压痛已固定在右下腹 [单选题]筛查新生儿先天性甲状腺功能减低症最常见的方法是:( )
A.TRH刺激试验 B.血清T4、TSH C.干血滴纸片测定TSH D.骨龄测定 E.放射性核素检查 我来回答: 提交
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