A Researcher Wants to Knock Down Gene Expression in Mouse

A researcher wants to knock down gene expression in mouse embryos at 12 days of development.Which approach could be used to accomplish this?

A) Injection of morpholinos into the two-cell embryo
B) Injection of RNAi into the two-cell embryo
C) Breeding of two transgenic mice, one with the gene of interest flanked by LoxP sites and another with an inducible promoter driving cre recombinase, and treat pregnant females at the desired time with an appropriate reagent such as Tamoxifen
D) Breeding of two transgenic mice, one with the gene of interest flanked by LoxP sites and another with the appropriate tissue-specific promoter driving cre recombinase
E) Generating a transgenic mouse using mutated DNA homologous to the desired target site in the gene of interest