module X
class A
@@a = 1
@@b = 0
def method_1
@@a = @@b
end
def A.method_2
@@a = 2
end
end
class B < A
@@c = 0
def method_1
@@a = @@c
end
end
class C < A
@@d = 0
def method_1
@@a = @@d
end
end
class D < B
@@e = 0
def method_1
@@a = @@e
end
end
end