A couple comes to the physician for advice about contraception and family planning. The physician provides advice about various methods of birth control. While discussing the option of using an intrauterine device, a discussion of the process of implantation comes up. At what stage of embryonic development does an embryo normally begin to implant in the endometrium?

1. A)BlastocystGABARITO
2. B)Morula
3. C)Zygote
4. D)Four-cell stage
5. E)Trilaminar embryo