Correct Answer: A

Rationale: A blastocyst does indeed require external nourishment from the mother's body to continue developing and gaining mass. Without this external nourishment, the blastocyst would not be able to grow and develop properly. Therefore, the statement that a blastocyst gains mass only when it receives nourishment from outside is true. Choices B, C, and D are incorrect because they do not accurately reflect the dependency of a blastocyst on external nourishment for its development and growth.

Correct Answer: A

Rationale: Yes, neural tube defects can cause an elevation in AFP levels in the mother's blood. AFP levels are often used as a screening marker during pregnancy to detect neural tube defects. Choice B is incorrect because an elevation in AFP levels can indeed occur in the presence of neural tube defects. Choice C is not the best option as it leaves room for uncertainty when the relationship between neural tube defects and AFP elevation is well-established. Choice D is incorrect as neural tube defects are known to influence AFP levels in the maternal blood.

Correct Answer: C

Rationale: Turner syndrome is a chromosomal disorder in females characterized by short stature and underdeveloped ovaries, resulting in low estrogen production. This leads to symptoms such as delayed puberty and infertility. Choice A is incorrect because the chromosomal abnormality in Turner syndrome does not affect the thymine-cytosine ratio. Choice B is incorrect as females with Turner syndrome are typically shorter than average. Choice D is incorrect as Turner syndrome does not increase the likelihood of giving birth to twins.

Correct Answer: A

Rationale: The correct answer is A. Positioning the car seat at a 45-degree angle is crucial to prevent the baby's head from falling forward, which can obstruct the airway. Choice B is incorrect because the recommendation is to keep the car seat rear-facing until the baby reaches the height or weight limit set by the car seat manufacturer, typically beyond 12 months. Choice C is incorrect as the harness should be snugly placed at or below the baby's shoulders, not above. Choice D is incorrect as the retainer clip should be positioned at armpit level to secure the harness straps properly.

Correct Answer: A

Rationale: Nagele's Rule is a common method used to estimate the due date. To calculate it, subtract 3 months and add 7 days to the first day of the last menstrual period. In this case, if the last menstrual period started on July 10, subtracting 3 months (April) and adding 7 days gives an estimated due date of April 17. This is the correct answer. Choices B, C, and D are incorrect because they do not follow the Nagele's Rule calculation method.