You can hardly imagine the once clear canal _____ so seriously polluted that no fish can live in it. [ ]

A. have become  

B. having become  

C. to have become  

D. to become

含油污水中的胶体颗粒径（），主要由泥沙腐蚀结垢产物和微细有机物构成。

A.1.0³10～3μm

B.1.0³10-2～2μm

C.1.0³10-3～1μm

D.1.0³10-4～1μm