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
Which immunoglobulin crosses placenta maximally: 
Select and explain. 
A. IgG1, B. IgG2, C. IgG3, D. IgG4
A: IgG1
Answer: A: IgG1 
Explanation: IgG1 - max , IgG4 - minimum