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:

Answer: Option A