The answer is either the third or fourth option.
I want to go more with the fourth one though!!
Dr. Leonard Hofstader and Dr. Sheldon Cooper are the other two.
I believe that Howard Wolowitz is the only engineer.
Explanation:
During 1989 and 1990, the Berlin Wall came down, borders opened, and free elections ousted Communist regimes everywhere in eastern Europe. In late 1991 the Soviet Union itself dissolved into its component republics. With stunning speed, the Iron Curtain was lifted and the Cold War came to an end.
B- the aridity hypothesis