We can generalize two-pass multiway merge-sort to use more than two passes. On the first pass, we divide the file into as many groups as we can merge in one pass. Then, recursively sort each group, using as many passes as necessary, and finally merge the sorted groups. A file of 2000 blocks is to be externally sorted, using 6 main-memory buffers. How many passes are needed? How many runs remain at the last pass? Find the correct number in the list below.

	a)	The number of passes required is 3.
	b)	The number of passes required is 5.
	c)	The number of passes required is 6.
	d)	The number of runs at the last pass is 4.