ANS:A - cummulatively increases

In laminar film condensation on a vertical surface, the film thickness cumulatively increases from top to bottom. As the condensate forms and flows down the vertical surface, it accumulates and adds to the thickness of the film. At the top of the surface, the film thickness is minimal, but as it moves downwards, more condensate adds to the film, resulting in a cumulatively increasing film thickness. So, the correct statement is: "cumulatively increases."