S1: The heart is pump of life.

P : They have even succeeded in heart transplants.

Q : Nowadays surgeons are able to stop a patients heart and carry out complicated operations.

R : A few years ago it was impossible to operate on a patient whose heart was not working properly.

S : If heart stops we die in about five minutes.

S6: All this was made possible by the invention of heart-lung machine.

The Proper sequence should be:

Correct Option - A

Explaination