干髓治疗的原理是
A．要保留成形的根髓
B．要保留分解的根髓
C．要保留感染的冠髓
D．要保留感染的牙髓
E．要保留健康的根髓
参考答案：A
无面额股票的特点有（）。
A.发行或转让价格较灵活
B.便于股票分割
C.注明它在公司总股本中所占的比例
D.为股票发行价格的确定提供依据
We tried _____ to persuade him to stay home, but at last, he went to the construct site in spite of his illness.[ ]
A. in vain
B. in return.
C. in fact
D. in time
