Question 1: A. were used to staying (Explanation: This is the most natural way to express that astronauts used to stay inside their spaceships but now frequently work outside.)

Question 2: D. did not use to believe (Explanation: This phrasing indicates that people in the past held a different belief about the Earth's shape.)

Question 3: A. used to be thought (Explanation: This expresses the past view that tuberculosis was incurable.)

Question 4: B. used to die (Explanation: This indicates a higher mortality rate for babies from whooping cough in the past.)

Question 5: A. to work (Explanation: "Used to" with the infinitive "to work" suggests the girls are not accustomed to field work.)