Roadrunner is a start-up grocery delivery service. Customers use an app to order grocery and are guaranteed to receive their orders within 10 minutes. Roadrunner competes by offering a small range of cheapest grocery and having the lowest delivery fee. Which of the following is the best performance measure on the customer perspective of its balanced scorecard?

a.Order system downtime.

b.Proportion of deliveries that arrive at customers' location within 10 minutes.

c.% increase in product range.

d.Customer rating on delivery staff friendliness.

e.Proportion of delivery couriers who have completed a road safety training.