People who have studied ancient instruments are hoping to learn more about the culture that ______ this ancient flute.

A．produce

B．produced

C．is producing

D．was produced

乙型肝炎患者血清中检出抗-HBs说明

A．免疫耐受，病情迁延不愈
B．获得免疫，疾病已经恢复
C．肝炎痫毒在体内复制
D．病毒变异，仅查出抗—HBs
E．乙肝患者注射疫苗的结果