用酚酞指示剂滴定法测定水中游离二氧化碳时，滴定终点标准比色液为0.1mol/L（）溶液。
A.氢氧化钠
B.碳酸氢钾
C.碳酸氢钠
参考答案：C
单句改错（共5小题，共5分）
小题1:Each boy and each girl were given a chance to compete in the game.
小题2:Mary mustn’t be in the library, for she went to the hospital with her mother just now.
小题3:Great changes have been taken place in my hometown in the past ten years.
小题4:Seeing from the spaceship, the earth is a huge water globe.
小题5:It’s very cold outside. You’d better to put on more clothes.
为便于操作和保证背面焊道的质量，打底焊时，应使用较小的焊接电流。 ( )
