You can’t see things clearly through a telescope unless it is _____ correctly to your sight.

While the soldier’s idea was interesting, the system was too difficult to be ____.

(2013·湖北，23)While intelligent people can often________the complex, a fool is more likely to complicate the simple.

Joining the firm as a clerk，he got rapid promotion，and ________ as a manager.

Some people say that Mars should be protected as a wildlife reserve where we do everything possible to avoid pollution, on the _______ that life could exist on it.