慢性肾功能衰竭最早和最常见的症状是（）
A.血液系统表现
B.心血管系统症状
C.胃肠道表现
D.神经、肌肉系统表现
E.呼吸系统症状
参考答案：C
We must do what we can to ____________the river ______________.
A．protect; against polluting
B．stop; polluting
C．keep; being polluted
D．prevent; from being polluted
