The creation of the was important because it is reusable, lands like a normal airplane, and eliminates the need to create a brand new spacecraft each time humans are launched into space.

The creation of reusable rockets was important because - as the continuation of your sentence says, they are reusable, land like a normal airplane and because they eliminate the need to create brand new spacecrafts each time humans are/will be launched into space. 

The answer is letter c