Read this excerpt from "One Flu over the Cuckoo's Nest.”

That year, scientists found that a very simple mutation in one gene could make a virus very easy to transmit. The groups also found many combinations of genes that could make the virus spread faster and cause it to be more lethal. Hualan says that health officials now know what genes to monitor to warn of a dangerous combination ready to spread throughout the world. She also says her work tells vaccine researchers what genes to target: "The important thing is that insights from such studies will benefit disease control and prevention.”

The original controversy has not gone away. And unfortunately, scientists do not know how these lab-bred viruses compare to the way viruses act in communities. More research is needed to protect the public from worldwide outbreaks of bird flu, which could be devastating.

What best describes the key discovery of research in efforts to control diseases?

Scientists found out which genes to monitor to find signs of danger.
Scientists discovered a cure for all flu viruses.
Scientists concluded that flu viruses easily transfer.
Scientists still need to learn more in order to prevent epidemics.

In this excerpt, the key discovery of research that scientist have made in efforts to control diseases is that scientists have found out which genes they need to monitor in order to find signs of danger. This is expressed in the first line of the passage, in which we learn that scientists found that a very simple mutation in one gene could make a virus very easy to transmit.