D – finite. ‘Either … or …’ construction requires two contrasting words in the gaps. The only word with the opposite meaning for infinite is finite here.’Limited’ has a similar meaning, but it normally has the meaning of being low in quantity.
C – place. You have to be careful here not to fall for the usual FCE/CAE trap. Even though we are talking about time, the phrase is ‘to take place’, regardless of whether we talk about where or when it happened.
A – away. Here they are talking about how distant the last point of visibility is – or how far it is. We can’t phrase is at ‘5 kilometers far’.
A – at. The preposition ‘at’ is the only one that works in this context with the noun ‘distance’, e.g. ‘He was the best runner at the 500 meters distance’.
C – existed. Keep in mind that we are talking about an inanimate object, it is not alive. This leaves us with existed and survived as the two options. The last one should not be used as it implies certain difficulties that it had to go through, which is not stated here.
A – ability. Ability is something that you have from birth, while skill is something you acquire or develop as you live.
A – mysterious. ‘Mysterious’ means unknown and difficult to understand – exactly the word that would explain the many secrets of space. ‘Odd’ and ‘strange’ have pretty much the same meaning, but the focus on being unusual. ‘Questionable’ has a negative meaning of not being completely true or honest.
D – looking. The only word here that goes well with ‘at’ preposition.