An ingredient in coffee, known as RTC, has been found to inactivate common cold viruses in experiments. In previous experiments, researchers found that inactivated common cold viruses can convert healthy cells into cancer cells. It can be concluded that the use of coffee can cause cancer. Which one of the following, if true, most seriously weakens the argument?

Several teams of scientists performed the various experiments, and all of the teams had similar results.

The carcinogenic effect of RTC could be neutralized by the other ingredients found in coffee.

When RTC kills common cold viruses it weakens the immune system, and it might thus diminish the body’s ability to fight other viruses, including viruses linked to cancers.

If chemists modify the structure of RTC, RTC can be safely incorporated into medications to prevent the common cold.