When rescuers arrived
P : they had to wait several hours
Q : before the ground was
R : at the ruins
S : cool enough to stand on

The Proper sequence should be:

A. PQRS

B. QSPR

C. RPQS

D. SRPQ

Answer: Option C

Solution(By Examveda Team)

When rescuers arrived at the ruins they had to wait several hours before the ground was cool enough to stand on.