The question from the test:
The atmosphere ___________ to extend several hundred kilometers above the Earth.
b. has been proved
c. is proved
Sentences with the blank filled with each option can be found using Google in various materials for learning English, so maybe all of them are possible. However this answer https://ell.stackexchange.com/a/6513/10667 says:
The perfect version is used when you're talking about something proved in the past.
So I've chosen (b) and it was the wrong answer. What is the correct one?