The first injectable polio vaccine was developed by Jonas Salk in 1952. Which of the following concepts/processes lies at the very basis of this invention?

Growing viruses in cell cultures allow preparation of purified viruses for the manufacture of vaccines. The injectable polio vaccine developed by Jonas Salk was one of the first products mass-produced using cell culture techniques. This vaccine was made possible by the cell culture research of John Franklin Enders, Thomas Huckle Weller and Frederick Chapman Robbins, who were awarded a Nobel Prize for their discovery of a method of growing the virus in monkey kidney cell cultures.