Answer:
Correct answer is Chinese immigrants
.
Explanation:
First option is a complete nonsense as of course there is no scientific proof that aliens exist.
Second option is not correct as suffrage movement was not a problem for federal authorities, especially in this period.
Third option is also not correct, as this event had nothing to do with Red Scare.
Last option is correct as after the establishment of People's Republic of China, people from China, especially students who came to US in that period.
