Distinguished guests and friends, welcome to our school, _____the ceremony of the 50th Anniversary this morning are our alumni （校友） from home and abroad.

A．Attend

B．To attend

C．Attending

D．Having attended

现场用于汽轮发电机组的水平仪大致可分为（）。

A.机械水平仪、长条型水平仪

B.长条型水平仪、方框水平仪

C.机械水平仪、合像水平仪

D.合像水平仪、方框水平仪