question: Q:An 82-year-old woman is brought to the physician by her daughter because of a 3-day history of a runny nose, headache, and cough. The patient's grandson recently had similar symptoms. Her vital signs are within normal limits. Pulse oximetry on room air shows an oxygen saturation of 99%. Lungs are clear to auscultation. Testing of nasal secretions is performed to identify the viral strain. Electron microscopy shows a non-enveloped RNA virus with an icosahedral capsid. Binding to which of the following is responsible for the virulence of this virus?? 
  {'A': 'P antigen', 'B': 'CD21', 'C': 'ICAM-1', 'D': 'Sialic acid residues', 'E': 'Integrin'},