Correct Answer: D

Rationale: After mitosis, the genetic code is typically preserved and remains identical in the new cells. However, mutations can occur due to radiation or environmental influences, leading to changes in the DNA sequence and potentially altering the genetic code. Therefore, the correct answer is 'mutations.' Choices A, B, and C are incorrect because reductions, expulsions, and conceptions do not accurately describe the changes in the genetic code that can result from external factors. Mutations are the only option that reflects the alteration in the genetic code caused by external influences, making it the correct choice in this context.

Correct Answer: A

Rationale: A low sperm count or lack of sperm is indeed one of the most common causes of infertility in men. Factors such as hormonal imbalances, genetic issues, reproductive anatomy problems, and lifestyle factors can also contribute to male infertility. Choice B is incorrect because a low sperm count is a prevalent issue among men facing infertility, making it a common problem. Choices C and D are incorrect as they do not accurately reflect the prevalence of low sperm count as a cause of infertility in men.

Correct Answer: C

Rationale: The correct answer is C. The development of arms and legs occurs during the critical period of the fourth to eighth weeks of pregnancy. This timeframe is crucial for the formation of limbs and other key body parts. Choices A, B, and D are incorrect because the development of the lungs, heart, and stomach respectively occurs at different stages of fetal development and is not primarily associated with the fourth to eighth weeks of pregnancy.

Correct Answer: A

Rationale: When assessing a preterm newborn at 32 weeks of gestation, healthcare providers should expect minimal arm recoil. This finding is common in preterm infants due to lower muscle tone. Choice B, a popliteal angle of less than 90°, is incorrect for this age group. Creases over the entire sole (Choice C) typically develop at term age, not at 32 weeks of gestation. Sparse lanugo (Choice D) is a normal finding in preterm infants but is not specific to those at 32 weeks of gestation.

Correct Answer: B

Rationale: The correct answer is B. Cystic fibrosis is a genetic disorder that causes the body to produce thick, sticky mucus. This mucus can clog the airways in the lungs and obstruct the pancreas, leading to severe respiratory and digestive problems. Choice A is incorrect because uncontrollable muscle movements and personality changes are not typical symptoms of cystic fibrosis. Choice C is incorrect because cystic fibrosis does not directly cause red blood cells to clump together and obstruct small blood vessels. Choice D is incorrect because cystic fibrosis primarily affects the respiratory and digestive systems, not the central nervous system.