高速铁路正线应采用（）无缝线路，到发线应采用无缝线路。无缝线路应具有足够的强度和稳定性。
参考答案：跨区间
When I talked with my grandma on the phone, she sounded weak, but by the time we ____ up, he voice had been full of life．
A．were hanging
B．had hung
C．hung
D．would hang
循环冷却水的沉积物控制中，沉积物控制包括______，而黏垢控制往往与微生物控制分不开。
A．结垢控制
B．污垢控制
C．腐蚀控制
D．水中离子控制
