Which of the following is an example of an opportunity cost?

	a.	The cost of a report done 3 years ago to investigate the potential of a new plant and the permits required to build it.
	b.	A soft drink company introduces a new drink which reduces sales of one of their existing soft drinks.
	c.	Apple's investment in the iTunes music store boosted sales of its iPod.
	d.	A firm has a vacant store that can be used for introducing a new store for the project. If the new store is not introduced, the firm could rent the store space for $3000.