Final answer:
The advertising budget and product sales increase rapidly during the growth stage of the product life cycle, as demand rises and companies invest in advertising to capture market share.
Step-by-step explanation:
The advertising budget and product sales both increase rapidly in the growth stage of the product life cycle. During this phase, demand for the product begins to accelerate and firms typically increase spending on advertising to maximize market share and consumer awareness. As a result, sales volumes expand significantly. The introduction stage is usually characterized by lower sales and high costs, including marketing, as the product is new to consumers. The maturity stage is when market saturation begins, leading to fiercer competition and potential reduction in prices. Lastly, the decline stage shows waning sales as the product loses consumer interest or becomes obsolete due to new technologies or trends.