题干
After hard training for a long time, he ____________ the records.
A：broke
B：achieved
C：invented
D：completed
答案(点此获取答案解析）
A
After hard training for a long time, he ____________ the records.
A：broke
B：achieved
C：invented
D：completed
2CrO42-＋ 2H+的平衡，其中Cr2O72-呈橙色，CrO42-呈黄色，向该平衡体系中滴加饱和NaOH溶液时，颜色的变化情况是（ ）