Which of the following is true?

	a.	All option implied volatilities tend to move by the same amount from one day to the next.
	b.	The implied volatilities of long-dated options tend to move by more than the implied volatilities of short-dated options.
	c.	The implied volatilities of short-dated options tend to move by more than the implied volatilities of long-dated options.
	d.	Sometimes B is true and sometimes C is true