Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage.

Why does Man want to go to other planets (1)_______ the solar system? Just for adventure? True, it is (a/an) (2) ________ in space travel.  But a (3) __________to other planets would also be (4) __________. For example, space stations could be built that would give us (5) ____________information about the weather. In space stations (6) ___________around the earth, Man could live and study the cloud formation on (7) ________surface. These formations could help us (8) ________the weather in any part of the world at any time. Such information would be (9) ______ to pilots, to ship captains, and even to farmers who must set dates for planting and (10) ________.

it is (a/an) (2) _________ in space travel.