The following six sentences come from a paragraph. The first and the last sentences are given. Choose the order in which the four sentences (PQRS) should appear to complete the paragraph.
S1: In 1668 an important discovery was made.
S6: That was the beginning of the end of the theory of spontaneous generation of higher plants and animals.
P: He put some rotting meat and fish in open jars and watched them.
Q: When he covered the jars with muslin, he found that flies came and laid their eggs on the muslin, but no maggots developed on the meat.
R: In time, he noticed that flies came and laid their eggs in the meat and the maggots hatched from the eggs.
S: An Italian physician named Redi decided to test the idea that worms were generated spontaneously in rotting meat.
The proper sequence should be: