In the past few years, My Heart Will Go On was a popular song among young people, ____ were often heard singing it at parties．

A．they

B． that

C． who

D．which

根据动植检专业进行分类，分别设立签证官和高级签证官两个层级，申请高级签证官资质的必须条件是（）

A.国外预检经历

B.行政职务

C.已取得签证官资质

D.学历