Final answer:
To alter the setting time of alginate irreversible hydrocolloid impression material, you can adjust the water temperature, with warmer water shortening and cooler water lengthening the setting time, or add a setting accelerator.
Step-by-step explanation:
An acceptable method for altering the setting time of alginate irreversible hydrocolloid impression material is A) Adjusting water temperature during mixing. Changing the temperature of the water used can influence the setting time. Warmer water accelerates the setting reaction, resulting in a faster set, whereas colder water slows down the setting reaction, making it set more slowly. However, options B) and C), which suggest increasing or decreasing the powder-to-water ratio, would likely compromise the material's properties and are not recommended methods for adjusting setting time. D) Adding a setting accelerator is indeed another viable approach to alter the setting time if specially designed additives are used for this purpose.