Although medical science ________ control over several dangerous diseases, what worries us is that some of them are returning．
A.achieved
B.has achieved
C.will achieve
D.had achieved
网友回答
B解析现在完成时表示过去发生的事对现在造成的结果，表示动作已经完成。根据所提供的情景“what worries us that some of them are returning”可判断出一些危险的疾病已经得到了控制，但有它们中的一些疾病又开始传播。