Correct Answer: C

Rationale: The correct answer is 'Diabetes mellitus' because it is a multifactorial disease, influenced by both genetic predisposition and environmental factors. Cystic fibrosis (choice A) is primarily a genetic disorder caused by mutations in the CFTR gene. Down syndrome (choice B) is due to an extra copy of chromosome 21. XYY syndrome (choice D) is a genetic condition where males have an extra Y chromosome. These conditions are not considered multifactorial as their origins are primarily genetic.

Correct Answer: C

Rationale: Acyclovir is the antiviral medication specifically used to treat herpes simplex virus infections, including genital herpes caused by herpes simplex virus type 2. Metronidazole (Choice A) is an antibiotic used for different types of infections, but not for viral infections like herpes. Penicillin (Choice B) is an antibiotic effective against bacterial infections, not viruses like herpes. Gentamicin (Choice D) is an antibiotic mainly used to treat bacterial infections, not viral infections like herpes.

Correct Answer: A

Rationale: The correct answer is A: 'A Rh-negative mother who has an Rh-positive infant.' In cases where the newborn is born post-term, the mismatched Rh factor between the mother (Rh-negative) and the infant (Rh-positive) can lead to hemolytic disease of the newborn. This condition occurs when maternal antibodies attack fetal red blood cells, causing hemolysis. This can result in jaundice, anemia, and other serious complications for the infant. Choices B, C, and D are incorrect because they do not reflect the mismatched Rh factor scenario that poses a risk for hemolytic disease of the newborn.

Correct Answer: D

Rationale: The correct answer is Monozygotic (MZ) twins. Monozygotic twins, also known as identical twins, share 100% of their genes because they originate from the same fertilized egg that splits into two. Fraternal twins (choice B), also known as dizygotic (DZ) twins (choice C), result from two separate fertilized eggs and share approximately 50% of their genes. Biovular twins (choice A) is not a term used in genetics and does not describe a type of twinning.

Correct Answer: B

Rationale: Individuals with cystic fibrosis have a genetic disorder that causes mucus to be thick and sticky, leading to blockages in the lungs and digestive system. This mucus buildup makes them more susceptible to severe respiratory infections, which can ultimately result in premature death in their 20s. Tay-Sachs disease (Choice A) is a genetic disorder that affects the nervous system, not typically causing respiratory infections. Turner syndrome (Choice C) and Klinefelter syndrome (Choice D) are chromosomal disorders that do not directly lead to the respiratory issues observed in cystic fibrosis.