Prior to Using PCR to Introduce Mutations into DNA in Vitro,what

Multiple Choice

Prior to using PCR to introduce mutations into DNA in vitro,what was a common method of mutagenesis used by scientists?

A) Self-fertilization of plants or inbreeding of animal models
B) Chemicals to induce mutations
C) Physical manipulation of DNA (e.g.vortexing)
D) Using only old parents to set crosses in plants and animals