Correct Answer: D

Rationale: Severe coughing spells are a hallmark clinical manifestation of pertussis. Pertussis, also known as whooping cough, is characterized by paroxysms of rapid, consecutive coughs followed by a distinctive 'whoop' sound as the patient gasps for air. This intense coughing can lead to vomiting, exhaustion, and sometimes a characteristic 'whoop' sound. Inspiratory stridor (Choice B) is more commonly associated with croup, not pertussis. Nasal congestion (Choice C) is not a typical feature of pertussis. While a cough is present in pertussis, the specific type of cough described in Choice A (dry, hacking cough) is not the predominant feature observed in pertussis.

Correct Answer: C

Rationale: Abnormal heart sounds could indicate a congenital heart defect, which is common in infants with Down syndrome.

Correct Answer: A

Rationale: The correct answer is A: nondisjunction. Trisomy 21, also known as Down syndrome, is caused by nondisjunction, which is an error in cell division leading to an extra copy of chromosome 21. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. Choices B, C, and D are incorrect. X-linked recessive inheritance refers to genetic disorders carried on the X chromosome, genomic imprinting involves gene expression based on parental origin, and autosomal dominant inheritance relates to disorders caused by a dominant gene on one of the non-sex chromosomes. In the case of trisomy 21, the cause is specifically related to the error in chromosome division, making nondisjunction the most appropriate answer.

Correct Answer: D

Rationale: Recognizing signs of hypoglycemia is crucial for managing type 1 diabetes mellitus and preventing complications.

Correct Answer: A

Rationale: In this scenario, the patient is experiencing airway compromise due to the fall and potential oropharyngeal obstruction from bleeding. Performing a jaw-thrust maneuver with head stabilization helps maintain the airway patency. The next step should be to suction the oropharynx to clear any blood or secretions, which can obstruct the airway and lead to aspiration. Inserting a nasopharyngeal airway may worsen bleeding or cause further injury to the patient's airway. Initiating positive pressure ventilations can be ineffective if the airway is not cleared first. Administering oxygen via mask is not the immediate priority; ensuring a patent airway by suctioning takes precedence.