Consider the concentration, C, (in mg/liter) of a drug in the blood as a function of the amount of drug given, x, and the time since injection, t. For $0 \leq x \leq 5$ mg and $t \geq 0$ hours, we have $$C = f(x,t) = 28te^{-\left(5-x\right)t}$$

$f(2,3) =$

Give a practical interpretation of your answer: $f(2, 3)$ is
A. the change in concentration of a 3 mg dose in the blood 2 hours after injection.
B. the amount of a 3 mg dose in the blood 2 hours after injection.
C. the amount of a 2 mg dose in the blood 3 hours after injection.
D. the concentration of a 3 mg dose in the blood 2 hours after injection.
E. the change in concentration of a 2 mg dose in the blood 3 hours after injection.
F. the concentration of a 2 mg dose in the blood 3 hours after injection.