What will happen when variable costs rise in a perfectly competitive industry? Selected answer will be automatically saved. For keyboard navigation, press up/down arrow keys to select an answer. The number of firms will eventually increase, but the existing firms will cut back production in the short run. b C d The number of firms will eventually decrease and the existing firms will cut back production in the short run. The number of firms will eventually decrease, but the existing firms will expand production in the short run. The number of firms will eventually increase and the existing firms will expand production in the short run.