人眼的“白眼球”和“黑眼球”，实际上分别指的是（ ）
A．虹膜和角膜
B．角膜和巩膜
C．角膜和虹膜
D．巩膜和虹膜
答案：D
--- Has your uncle ever been to Tibet ?
---___________________________.
A. No, he didn't B. No, he haven't C. No, never
-3+2= [ ]
A．1
B．-1
C．5
D．-5
