Study the given Venn diagram carefully. P - Animals breathing through lungs only. Q - Animals breathing by skin only. R - Animals breathing by gills. X - Animals breath by skin and gills both. Y - Animals breath by skin and lungs. Z - Animals breath by lungs and gills. Then, which alphabet represents frog?

• A.  Y   
• B.  X     
• C.  Z    
• D.  P