Nokea
Dichorionic-diamniotic twins result from separation of embryonic cells at the:
Correct Answer: A
Rationale: The correct answer is A: Four-cell stage. Dichorionic-diamniotic twins occur when the embryo splits into two separate embryos very early in development, typically at the four-cell stage. At this stage, each embryo will have its own chorion and amnion, leading to separate placentas and amniotic sacs. Choices B, C, and D occur later in development and do not result in the formation of two separate embryos with their own chorion and amnion, making them incorrect for the scenario of dichorionic-diamniotic twins.