What is the difference between the second-generation IVF (Intracytoplasmic Sperm Injection) and the first-generation IVF-ET (in vitro fertilization-embryo transfer)? A、In vitro fertilization B、A single sperm is injected directly into an egg by a micromanipulation system in order to achieve fertilization. C、Preimplantation embryos are genetically tested for chromosomes or specific disease-causing genes D、Embryos need to be frozen
