All the given options are adjectives.
Option D - 'Fair' means 'justified or equitable' and this adjective is appropriate for the given sentence because the context is about the selection of a team which should be just in all means, ie 'fair'.
Option A - 'Convenient' means 'suitable', Option B - 'Absolute' means 'complete or entire', Option C - 'Challenging' means 'demanding or testing'. None of which suits the given context.
Therefore, the appropriate option to complete the given sentence is Option D - Fair.
The completed sentence, thus, becomes: It is important that you select the team in a fair way.