Final answer:
Avery's experiments showed that DNA is the hereditary material because transformation is prevented when DNA is destroyed by specific enzymes.
Step-by-step explanation:
Avery's experiments showed that transformation is prevented by DNA-destroying enzymes. The experiments, conducted by scientists Oswald Avery, Colin MacLeod, and Maclyn McCarty, found that when DNA within a bacterial extract was degraded using specific enzymes, the ability to transform non-virulent R strain bacteria into virulent S strain was lost. This finding was pivotal because it indicated that DNA, and not proteins or RNA, was the transforming principle, showing that DNA was responsible for heredity. Despite the strength of their results, many scientists were skeptical and believed that proteins, which are more complex molecules, were more likely to carry genetic information. It wasn't until the Hershey-Chase experiment in 1952 that there was wider acceptance of DNA as the genetic material.