Hello,
The answer is option C (D) "more than 50,000".
Reason:
Over 58,000 Americans died in the Vietnam War. Also there was 2 million civilians died on both sides but the number of Americans died lead up to the number: 58,200 who died therefore the answer should be option A because of the reasons above.
If you need anymore help feel free to ask me!
Hope this helps!
~Nonportrit