I saw him, but he didn't see me,            ? [ ]

A. didn't I

B. did he

C. did I

D. didn't he

中国人是黑眼睛的，有的外国人是蓝眼睛的，这种眼睛的色素存在于 [ ]

A．角膜

B．虹膜

C．晶状体

D．视网膜