For years, doctors millions of patients’ lives with the help of mi

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问题 For years, doctors ______ millions of patients’ lives with the help of ______ microscopes.

选项 A、have saved
B、are saving
C、will save
D、were saving

答案 A

解析本题考查对时态的掌握。由时间状语For years可知，本题应该用现在完成式。

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For years, doctors ______ millions of patients’ lives with the help of ______ mi