What is the "brain drain" concept all about?

Multiple Choice

All of the statements are true.

Albert Einstein and Warner Von Braun were two top$-$tier German scientists that escaped Hitler's Nazi Germany during World War II with the help of U$.$S$.$ OSS secret agents. They both contributed to America's scientific advances in physics and space travel. This is a good example of a successful brain drain story that benefited the United States.

$$ During the $1940\text{'}$s$,1950\text{'}$s and $1960\text{'}$s$,$ the U$.$S$.$ State Department pursued a policy of finding and attracting large numbers of well$-$educated, talented and productive immigrants who were willing to work. They also had to sign