用于改善复合层的牙本质表面处理剂是()。
A.乙二胺四乙酸二钠水溶液
B.37%磷酸水溶液
C.丙酮酸
D.枸橼酸
E.5.3%草酸铁水溶液
参考答案:E
No one can imagine the difficulty he had _______ his son to get rid of the habit of playing computer games.
A.persuading
B.to persuade
C.persuaded
D.persuade
现在有住宿生若干名,分住若干间宿舍,若每间住4人,则还有19人无宿舍住;若每间住6人,则有一间宿舍不空也不满,求住宿人数和宿舍间数.