角膜约占眼球壁外膜的前1／5，角膜无色、透明、无血管，感觉神经末梢非常丰富。
参考答案：错
By the time he ____ at the party, all the other guests ____ playing games.
A．arrived; had begun
B．arrived; began
C．had arrived; began
D．had arrived; have begun
医疗价格管理的要求有哪些？
