On 12 October 2006 Rebecca bought a zero-coupon bond with maturity date of 12 October 2011. Rebecca sold the bond on 12 October 2008. The table below shows zero-coupon rates as at 12 October 2006 and 12 October 2008.

term(years)	zero-coupon rates (% pa) on 12 October 2006	zero-coupon rates (% pa) on 12 October 2008
1	7.90	10.10
2	7.75	10.25
3	7.70	10.35
4	7.66	10.40
5	7.64	10.45

Rebecca's holding period rate of return is closest to:

a) -6.239% pa

b) 3.699% pa

c) 7.535% pa

d) 7.75% pa