The biggest whale is ______ blue whale, which grows to be about 29 meters long-the height

of ______ 9-storey building. [ ]

A. the; the

B. a; a

C. the; a

D. a; the

眼球的结构与功能：         （无色透明，可透光） 虹膜（中央是         ） 瞳孔（         ）  晶状体（凸透镜、折射光） 玻璃体 视网膜  脉络膜            （保护作用）  视网膜