Show the stack with all activation record instances, including static and dynamic chains, when execution reaches position 1 in the following skel- etal program. Assume bigsub is at level 1. function bigsub() { function a(flag) { function b() { ... a(false); ... } // end of b ... if (flag) b(); else c(); ... } // end of a function c() { function d() { ... <1 } // end of d ... d(); 468 Chapter 10 Implementing Subprograms 4. ... } // end of c ... a(true); ... } // end of bigsub The calling sequence for this program for execution to reach d is a. bigsub calls a b. a calls b c. b calls a d. a calls c e. c calls d