Paula was ..... a child, accepting with out a question, every thing she was told.

Option A: Reticent is someone who does not reveal one's own thoughts and feelings; while this might relate to the part about Paula not questioning, this does 

Option B: Taciturn is a person who is reserved in speech and says little. Although this would fit with the part about Paula not questioning, this does not reflect her tendency to believe everything she was told. 

Option C: Recalcitrant means someone who has an uncooperative attitude and hence would be the exact opposite of what is needed in the sentence. 

Option D: Credulous refers to someone always ready to believe in things. This would be the most apt word for Paula as described in the sentence. 

Therefore, Option D is the correct answer.