12. Consider the following program, written in JavaScript-like syntax // main program var x, Y, Z function subl ) var a, Y. Zi function sub2 () var a, b, z; function sub3 ) var a, x, w; Given the following calling sequences and assuming that dynamic scop ing is used, what variables are visible during execution of the last subpro- gram where it is declared a. main calls subl; subl calls sub2; sub2 calls sub3. b. main calls subl; subl calls sub3 c. main calls sub2; sub2 calls sub3; sub3 calls subl. d. main calls sub3; sub3 calls subl. e. main calls subl; subl calls sub3; sub3 calls sub2 f. main calls sub3; sub3 calls sub2; sub2 calls subl. activated? Include with each visible variable the name of the unit