Asbestos is MOST dangerous when it A) is used as insulation. B) is wrapped around heating and water pipes. C) gets wet. D) crumbles and becomes airborne.

To determine when asbestos is most dangerous, let's analyze each option: A) **Is used as insulation.** While asbestos insulation can be hazardous, it is not the most dangerous state. If it remains intact, it poses a lower risk. B) **Is wrapped around heating and water pipes.** Similar to insulation, if the asbestos is intact and undisturbed, it is less of a risk. However, if it becomes damaged, it can release fibers. C) **Gets wet.** Wet asbestos is generally less likely to become airborne. Water can help to keep the fibers from becoming airborne, making it less dangerous in this state. D) **Crumbles and becomes airborne.** This is the most dangerous condition for asbestos. When asbestos materials crumble, they release tiny fibers into the air, which can be inhaled and pose serious health risks, including lung diseases and cancer. Based on this analysis, the correct answer is: **D) crumbles and becomes airborne.**