捕收剂、起泡剂的用途如何？
参考答案：
起泡剂主要提高矿物表面疏水性，使要浮的矿粒附着于气泡上。
捕收剂主要提高气泡的稳定性与寿命。
____ about the student, the teacher called his parents to find out why he was so absent-minded in class. [ ]
A. Concerned
B. Concerns
C. Concerning
D. Concern
窦房结细胞（）
A.0期去极化速度慢
B.动作电位幅度小
C.最大舒张电位绝对值较小
D.4期自动去极化较慢
E.属慢反应自律细胞
