Which of the following is not one of the conditions under which negotiation is effective?

	a.	When the buyer requires early supplier involvement.
	b.	When the specifications or requirements are clear to the seller.
	c.	When the supplier cannot determine risks and costs.
	d.	When the supplier requires a long period of time to develop and produce the items purchased.
	e.	When the purchase requires agreement about a wide range of performance factors, such as price, quality, delivery, risk sharing, and product support