public AmVi(String tu)
{
this.am_tiet = new CaiDat(tu);
this.phien_am = String.Empty;
khoiTaoDanhSachPhienAm();
}
public AmVi()
{
am_tiet = new CaiDat();
phien_am = String.Empty;
khoiTaoDanhSachPhienAm();
}