在计划性预防检修的总体框架下实行（）、（）、集中修是目前国内外铁路车辆部门主要采用的检修体制。
参考答案：状态修；换件修
等腰三角形的周长为24，那么腰长x的取值范围为（ ）
A．0＜x≤8
B．0＜x＜6
C．0＜x＜12
D．6＜x＜12
In order to perform the monitor function, language learners have to satisfy at least three conditions: sufficient time to monitor his production, focus on form and a clean knowledge of ______.
A. mother language B. vocabularyC. phonetics D. the rule of the target language
