Although the whole team acted in unison, each member was ......... for a/an ........ of the production process.
This is the given sentence. We are looking for words that highlight the individuality and the fact that each person on the team was responsible for the success of the show and the production process. 
We see that Option B fits this need. 
Filling in with option B tells us that while the whole team acted together, each member was responsible for an element in the production process.