Answer:
b. Hall knew that growing outrage among the American public would help Britain’s cause.
Step-by-step explanation:
B is the CORRECT answer because the following sentence "Hall reminded them that outrage was growing in America" indicates that Hall was aware of this situation and it would be in favour or Britain interests to join forces against Germany. Answers A, C and D are incorrect given that in any section of the excerpt such information is implicitly or explicilty expressed.