If I were from the past century, what scientific wonder would you first show me?

Question

If I were from the past century, what scientific wonder would you first show me?

Answer 1

I wouldn't show you anything because it would change my present... :)

Answer 2

Penicillin!.

Answer 3

Since the past century is the 20th, I wouldn't know of many "breakthroughs" unveiled this century that weren't already in development during the latter part of the 20th century.