TOEFL Reading: ETS-TOEFL阅读机经 - 6PWR9QV8LE7HQ5XPL$

According to paragraph 5, why did Oswald Avery and his colleagues treat the transforming extract in a variety of destructive ways A. They hoped to destroy the virulent part of the transforming extract. B. They wanted to identify the substance responsible for the transforming activity. C. They wanted to identify which methods would destroy particular substances in the transforming extract. D. They needed to determine which treatments were most successful in destroying DNA.