Consider the concentration C $($in mg$/$litre$)$ of a drug in the blood as a function of the amount of drug injected, x$,$ in mg$,$ and the time since injection, t$,$ in hours. For $0$x$5$ mg and t$0$ hours, we haveC$=$f$($x$,$t$)=22$xte$5$t$.$

Calculate the following:

f$(2,5)=$

Give a practical interpretation of your answer. Choose the best option.

f$(2,5)$ is:

A$.$ the amount of a $5$ mg dose in the blood $2$ hours before injection.

B$.$ the concentration in the blood $2$ hours after injection of a $5$ mg dose.

C$.$ the concentration in the blood $5$ hours after injection of a $2$ mg dose.

D$.$ the half$-$life of a $2$ mg dose in the blood $5$ hours after injection.

E$.$ the change in concentration of a $5$ mg dose in the blood $2$ hours after injection.

F$.$ the change in concentration of a $2$ mg dose in the blood $5$ hours after injection.