This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
A child present with recurrent episodes of sinopulmonary infection by bacteria with polysaccharide rich capsule. Deficiency of which of the following immunoglobulin subclasses should be specifically investigated - 
Select and explain. 
A. IgA, B. IgG 1, C. IgG2, D. IgA + IgG2
D: IgA + IgG2
Answer: D: IgA + IgG2 
Explanation: None