-Who is talking?
-_______[ ]
A. It's a bird.
B. It's Danny.
C. He's reading.
答案:B
下列哪一项不是形成近视的原因?( )
A.晶状体的凸度过大
B.物象落在视网膜的后方
C.物象落在视网膜的前方
D.眼球的前后径过长
硅藻门有何价值?