分置式液压系统
参考答案：
指液压油泵、分配器、液压油缸分开布置的液压系统
We must do something to ________ the factories sending out poisonous gases so as to keep the city clean and beautiful.
A．keep
B．protect
C．permit
D．prevent
土壤肥力的生态相对性要求我们在土壤管理中做到“适地适树”。( )
