As a child, you contracted hand, foot, and mouth disease, which is caused by a virus. several years later, your sibling also contracted the same virus. why don't you get sick a second time?

you have antibodies that already recognize the virus.
white blood cells released histamines and killed the virus.
your skin prevented the virus from entering your body.
stomach acid inactivated the virus, preventing its spread.

The answer is A.) You have antibodies that already recognize the virus

Viruses and diseases are always changing. When we get sick with say the flu, a virus, or the cold of sorts, our body attacks it until it fights off the disease. You can't get sick from the same strand of sickness because once your body defeats the virus, it knows how to protect the body from it because of the antibodies, so the virus ends up evolving to get past your immune system again.

I hope this helped! Have a wonderful day :)

Gravitational force i believe