$6.$ Assume that the riskless rate of interest is $5\%$ per year. If there are no arbitrage opportunities in the futures markets and Stock XYZ pays dividends, which of the following cannot be a valid pair of spot and $12-$month futures prices for Stock XYZ$?$

$4)$ Spot $=$ $$45,$ Futures $=$ $$45\mathrm{.}00$

B$)$ Spot $=$ $$45,$ Futures $=$ $$47\mathrm{.}75$

C$)$ Spot $=$ $$45,$ Futures $=$ $$44\mathrm{.}75$

D$)$ Spot $-$ $$50,$ Futures $=$ $$51\mathrm{.}50$