溃疡性结肠炎的内镜下表现是（）

A.黏膜隆起呈息肉状、有蒂

B.黏膜广泛充血、水肿、糜烂，表面有脓苔

C.黏膜呈鹅卵石样增生，肠腔明显狭窄

D.跳跃式分布的纵形或匍行性深溃疡

E.黏膜破裂出血

It's ten years since the scientist     _ on his life's work of discovering the valuable chemical.     [ ]

A. made for                    

B. set out      

C. took off                    

D. turned up