Two blocks A and B are pressed against a vertical wall by applying a horizontal force 'F' as shown in the figure. There is no friction between A and B. Then
a) Both the blocks A and B can be at rest for any magnitude of F
b) B can be at rest A moves down for smaller magnitude of F
c) Both A and B will move down for smaller magnitude
d) A can be at rest and B moves down for larger magnitude of F