12. Consider the following program, written in JavaScript-like syntax: // main program var x, Y. z; function subl var a, y,z function sub2 ) var a, b, z function sub3 ) vara, x, w; Given the following calling sequences and assur ing is used, what variables are visible during execution of the last subpro- gram activated? Include with each visible variable the name of the unit 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