For years,doctors____millions of patients' lives with the help of microscopes.A.have saved B.are saving C.will save D.Were saving为什吗选第一个呢

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For years,doctors____millions of patients' lives with the help of microscopes.A.have saved B.are saving C.will save D.Were saving为什吗选第一个呢
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For years,doctors____millions of patients' lives with the help of microscopes.A.have saved B.are saving C.will save D.Were saving为什吗选第一个呢
For years,doctors____millions of patients' lives with the help of microscopes.
A.have saved B.are saving C.will save D.Were saving为什吗选第一个呢

For years,doctors____millions of patients' lives with the help of microscopes.A.have saved B.are saving C.will save D.Were saving为什吗选第一个呢
选项是A.
为什么选第一个,因为For years表示从过去算起到现在(还可以继续)“多年”.关于现在完成时的概念,到百度查询一下就清楚了.

选A 。For years现在完成时的标志。

语法问题啊,因为它前面是for years,就是说有了几年... 还有一件事,那个patients' live 应该是patients' life 哦