SI : Science has already conferred an immense boon on mankind by the growth of medicine. S6: The general death rate in 1948 (10-8) was the lowest ever recorded up to that date. P : It has continued ever since and is still continuing. Q : In the eighteenth century people expected most of their children to die before they were grown up. R : In 1920 the infant mortality rate in England and Wales was 80 per thousand; in 1948 it was 34 per thousand. S : Improvement began at the start of the nineteenth century, chiefly owing to vaccination. The proper sequence should be
- AR P Q S
- BQ S P R
- CS Q R P
- DP Q S R
Explanation
S1 credits medicine with conferring a boon on mankind. Q sets the grim 18th-century baseline, S begins the improvement story (19th-century vaccination), P notes that the improvement continued, and R gives the 1920–1948 statistics supporting S6's record-low 1948 death rate. The order Q S P R (B) is the only coherent chain. Hence the answer is B.