Over the past decades, sea ice _______ in the Arctic as a result of global warming. [ ]

A. had decreased    

B. decreased  

C. has been decreasing  

D. is decreasing

抗HBs阳性可见于（）

A.乙肝病人恢复期

B.乙肝病人窗口期

C.慢性HBV感染者血清转换

D.注射乙肝疫苗后

E.既往感染过乙型肝炎病毒