—Have you heard of the blue whale?

—Yes. I know it's the world's largest _____.[ ] 

A. plant

B. animal    

C. bird

D. man

角膜各层中，损伤后不能再生的有（）

A.基质层

B.Bowman层

C.Descemet层

D.内皮细胞层

E.上皮细胞层