—Why does the lake smell terrible?  

—Because large quantities of water ________. [ ]

A. have polluted

B. is being polluted

C. has been polluted

D. have been polluted

中心暗点常见于下列疾病

A．球后视神经炎

B．视网膜色素变性

C．老年黄斑变性

D．中心性浆液性视网膜脉络膜病变

E．黄斑出血