The door opened and there    .

A．entering our English teacher

B．entered our English teacher

C．did our English teacher enter

D．our English teacher entered

液压系统的压力分级有低压、中压、中高压、高压、超高压五种，当系统压力为＞25－80kg/cm²时，称（）。

A、中压

B、中高压

C、高压

D、超高压