为什么直流PWM变换器-电动机系统比V-M系统能够获得更好的动态性能？
继发型肺结核好发于：（） ["两肺下叶背段或右肺中叶","两肺上叶尖后段或右肺中叶","两肺下叶","右肺中叶","两肺上叶尖后段或两肺下叶尖段"]
简述留置的法律特征。
Which layer of the OSI reference model uses flow control, sequencing, and acknowledgements to ensure that reliable networking occurs?（） [" data link"," network"," transport"," presentation"," physical"]
诱变时选择出发菌株时应考虑（）、（）、对诱变剂敏感、（）等问题。
学前教育肩负着（）学龄前儿童，促使他们在体、智、德、美各方面得到全面发展的任务。
