An investor purchases an eight$-$year, $6\mathrm{.}4\%$ annual coupon eurobond priced at par $($settlement: $15$ June $2031$; maturity: $15$ December $2039)$ and sells it after six years. Assuming interest rates rise by $100$ bps immediately after purchase, the investor$$s rate of return at the end of six years is:

A$.$lower than $6\mathrm{.}4\%.$

B$.$equal to $6\mathrm{.}4\%.$

C$.$higher than $6\mathrm{.}4\%.$