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

当飞机低速穿过温度低于-20°C左右云滴较小的云中，常形成（）.

A.雾淞

B.明冰

C.毛冰