Hello.
A. X-rays I don't think this is correct, since X-rays have been around since 1895 and computer have only been around since 1947.
B. Vaccinations is not correct because vaccinations have been around for quite sometime, not only that they don't really use computers. They are given to you through a needle, which most people call a 'shot.'
C. Gene mapping is the answer that I personally would go with, since you can take DNA from someone and test it and you can use it to do many things.
D. CAT scans have been around since 1967, and computer like I said above have been around since 1947. . . so this could be the answer, but this isn't the answer that I'd go with.
I hope this helped you!