下列预防性树脂充填操作中哪项是错误的

A．用手机去除龋坏组织，去除悬浮釉柱，作预防性扩展

B．彻底冲洗，干燥，隔湿

C．C型酸蚀用Ca（OH）2垫底

D．酸蚀合面及窝洞

E．用适当的树脂材料料充填，固化后在合面涂布一层封闭剂

________ doesn’t seem to have been much difficulty in solving the problem.

A．It

B．That

C．There

D．He