In case Customs duties are short--levied or not levied on import or export, the Customs may, within ______ after the date of payment of Customs duties or the date of relesse of the goods, recover the amount of Customs duties short-levied or not levied.

A．six months

B．one year

C．two years

D．four years

体液免疫初次应答时产生Ig的特征是：

A．抗体含量比再次应答高
B．抗体的产生持续时间较长
C．IgG出现较晚
D．抗体为高亲和力抗体
E．产生的抗体以IgG为主