John and james are identical twins. during the summer following their 15th birthday, they went on a vacation and stayed in a cabin with two of their cousins. one of the cousins came down with chicken pox during the vacation. chicken pox is caused by a virus. two weeks later, john came down with chicken pox. james, however, never developed any symptoms of the disease.

which of the following is the best explanation for the different responses john and james had to their exposure to the same disease?

1. james had a cold at the time he was exposed to the chicken pox virus. the cold virus had stimulated his body to produce lots of b cells, which were then also able to recognize and bind to the chicken pox viruses. john did not have a cold at the time he was exposed to the chicken pox.

2. even though john and james are identical twins, they produce different kinds of immune system cells. james had cytotoxic t cells that could recognize and destroy the chicken pox viruses, while john did not.

3. james had been exposed to chicken pox at an earlier age and developed the disease. his body produced memory cells that protected him from further infections of the disease. john did not get exposed to chicken pox at an earlier age.

4. john and james are not really identical twins. james inherited an immunity to chicken pox but john did not.