Initially activation stack is empty.
I have used A1, A2, B1, B2 for understanding purpose, which refers to A and B respectively.
Test()
{//Scope of Test begins. In activation record Test is added
A()
{
//Scope of A begins.
// Activation stack: Test---> A
B1()
{
//Scope of B1 begins.
// Activation stack: Test---> A--->B1
A1()
{
//Scope of A1 begins
// Activation stack: Test---> A--->B1--->A1
}//Scope of A1 ends
//Activation record before y pt of execution Test---> A--->B1
At y point of execution
A2()
{
//New Activation record of A created
//Activation stack: Test---> A--->B1--->A2
}//Scope of A2 ends
}//End of scope B
//Activation stack: Test---> A
B2()
{
//Activation of B2 added
//Activation stack: Test---> A--->B2
}
}//End of scope A
//Activation Record before x point of execution: Test
At x point of execution
A()
{
//Activation Record: Test--->A
}
}//End of scope Test