Given below are four jumbled sentences. Pick the option that gives their correct order.
P. The Spanish flu, also known as the 1918 flu pandemic, was a deadly pandemic in recent history.
Q. It spread worldwide during the year 1918-1919.
R. The virus infected 500 million people - about a third of the world's population at the time.
S. The death toll was estimated to be at least 50 million worldwide, possibly as high as 100 million this makes it the severest pandemic in human history.