无齿曳引电梯采用永磁同步曳引机作为电梯的驱动系统，比传统曳引电梯有更多的优点是（）. ["体积小、重量轻","能耗低",".噪音小","载重量较大"] 呕血与黑便最常见于() ["胃底、食管静脉曲张破裂","十二指肠炎","慢性胃炎","急性胃黏膜病变","消化性溃疡"] 调整平衡系数可用（）方法. ["增加对重铁","减少对重铁","增加轿厢重量","加大曳引机电动机功率","减少轿厢重量"] 电梯井道安全门的门锁要符合下列（）的要求 ["在井道内不用钥匙能将门打开","不用钥匙能将门锁上","在井道外只能用钥匙才能将门打开","井道内应能将门反锁"] 若患者胸痛部位在胸骨中上段后方，并向左，肩部放射，最可能的疾病为() ["胸膜疾病","心绞痛","肋间神经病变","食管炎症","肋骨骨折"] 以下原因（），会使电梯不能启动.