The number of customers who dine at Eat and Den, a restaurant, varies during weekdays and weekends. On days when customer traffic is less, Eat and Den incurs losses because the food prepared on one day will not be fresh the next day. In this scenario, which of the following characteristics of services is the reason for Eat and Den's loss of revenue?

i. Intangibility 

ii. Variability 

iii. Heterogeneity 

iv. Perishability