A) there must be two host animals and two fertilized eggs B) a fertilized egg is collected from a donor mother and implanted into a host animal C) an egg is fertilized by in vivo fertilization and remains in the host animal to mature D) an embryo must be in a blastocyst stage in the host animals while the splitting takes place E) an unfertilized egg is collected from a donor mother and then fertilized in a dish by in vitro fertilization