题干
He was busy writing the exam paper, only once in a while to check the time.
A：to stop
B：stopping
C：to have stopped
D：having stopped
答案(点此获取答案解析）
B
Fe2+（aq）+B2-（aq）的平衡常数表达式为Ksp= c（Fe2+）·c（B2-），FeB在水中的沉淀溶解平衡曲线如图所示。下列说法错误的是（ ）