Which of the following is an example of heterogeneity of services?

a$.$

The customer service agent who contacted me last week was more helpful than the one who contacted me today

b$.$

The packaging of the pizza that I ordered today had a very different design and was made of recyclable paper

c$.$

The surgical instruments that doctors use in a New York hospital are the same as those used by doctors in the Miami hospital where I was examined

d$.$

The tire I bought at a Chicago service station came with a discount but lasted as long as another other tire