关于颅脑MRI技术叙述，下列错误的是

单项选择题The single acting cylinder is the simplest form. where pressure is applied to the full area of the piston head to move the load through piston rod extensionThe load causes rod _____ when the drive pressure is releaseD.A.contractionB.retractionC.expansionD.shrinkage

单项选择题架空线路同一档距内的同一相导线上的接头数不得超过()。