水中碱度实际指()离子的含量。
参考答案:氢氧根
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