During which period does the germinal period occur?

Correct Answer: C

Rationale: The germinal period lasts about two weeks and occurs during the first two weeks of pregnancy. This is the time when the fertilized egg implants into the uterus and begins to divide rapidly. It is followed by the embryonic period, which lasts from about week 3 to week 8 of pregnancy. Choice A is incorrect because the germinal period happens in the early stages of pregnancy, not the second trimester. Choice B is incorrect because the germinal period typically lasts about two weeks, not six. Choice D is incorrect because the germinal period is an early stage of pregnancy and not the final period of a 38-week pregnancy.

Correct Answer: B

Rationale: The correct answer is B: nervous system and skin. The nervous system, which includes the brain, spinal cord, and nerves, as well as the skin, develop from the ectoderm layer of cells during prenatal development. Choice A is incorrect because muscles and skeleton develop from mesoderm. Choice C is incorrect because the circulatory system and other internal organs develop from mesoderm and endoderm. Choice D is incorrect because the digestive system, lungs, urinary tract, and glands develop from endoderm.

Correct Answer: C

Rationale: During the second month of pregnancy, the heart of the developing fetus begins to develop separate chambers, forming the structure necessary for a fully functioning heart. This is a significant milestone in the prenatal development process. Choices A, B, and D are incorrect because the appearance of the umbilical cord as a primitive body stalk typically occurs around week 5-6, touch sensitivity extending to most of the body is more characteristic of the end of the second trimester, and the heartbeat is usually detectable through a stethoscope around the 18th to 20th week of pregnancy, not during the second month.

Correct Answer: B

Rationale: Brain weight increases tenfold from the twentieth week until birth. This rapid growth and development of the brain during the prenatal period is crucial for setting the foundation for future cognitive and neurological functions. Choices A, C, and D are incorrect because although they also undergo changes during prenatal development, none of them increase tenfold from the twentieth week until birth, unlike brain weight.

Correct Answer: B

Rationale: In the last weeks of pregnancy, most fetuses assume an upside-down position known as the head-down position or vertex presentation. This position is ideal for a smoother labor and delivery process as it helps the baby move through the birth canal. Fetal growth has already slowed down at this stage, so option C is incorrect. Option A is inaccurate as the fetus typically gains weight in the final weeks. Option D is incorrect because the fetus relies on the mother's immune system while in the womb.