Final answer:
Under J. Roswell Flower's administration, the missionary policy that was instituted required new missionaries to complete a course of study at an approved Bible institute.
Step-by-step explanation:
Under J. Roswell Flower's administration, the policy that was instituted was option (d). New missionaries were required to complete a course of study at an approved Bible institute. This policy ensured that new missionaries were adequately trained and prepared before being sent out to do missionary work. By completing a course of study, they would gain the necessary knowledge and skills to effectively spread the gospel and carry out their missions.