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

For years,doctors___ millions of patients’ lives with the help of microscopes. A: have saved B: are saving

For years, doctors ___ millions of patients’s lives with the help of microscopes. A: have saved B: are saving

So small () that the most powerful microscopes cannot detect them. A: are these particles B: were these particles C: these particles are D: these particles were

So small ______ that the most powerful microscopes cannot detect them. A: are these particles B: B. were these particles C: these particles are D: D. these particles were

For years, doctors ________ millions of patients’ lives with the help of microscopes. A: have saved B: are saving C: will save D: are saving

5.For years,doctors________millions of patients lives with the help of microscopes. A: A.saved B: B.have saved C: C.has saved D: D.were saving

5. For years, doctors ______ millions of patients’ lives with the help of microscopes. A: have saved B: are saving C: will save D: were saving