―________ you _________ the chief editor at the airport?

―No. He _______ away before my arrival.

A．Have; met; has driven

B．Had; met; was driven

C．Did; meet; had been driven

D．Have; met; was driven

某离子晶体晶胞结构如下图所示，x位于立方体的顶点，

Y位于立方体中心。试分析：

(1)晶体中每个Y同时吸引着__________个X，每个x同时吸引着__________个Y，该晶体的化学式为__________ 。

(2)晶体中在每个X周围与它最接近且距离相等的X共有 __________个。

(3)晶体中距离最近的2个X与1个Y形成的夹角∠XYX的度数为__________。