The Initial Volume of a Sample Is 100 μL $\frac{(400 \mu \mathrm{L})\left(\frac{25 \mu g}{\mathrm{~mL}}\right)}{100 \mu \mathrm{L}}$

The initial volume of a sample is 100 μL.It is diluted with saline by a factor of 4.The final volume is 400 μL.Testing the diluted sample finds an analyte concentration of 25 μg/mL.Which of the following expressions can be used to calculate the initial analyte concentration of this sample?

A) $\frac{(400 \mu \mathrm{L}) \left(\frac{25 \mu g}{\mathrm{~mL}}\right) }{100 \mu \mathrm{L}}$
B) $\frac{(100 \mu L) \left(\frac{25 \mu g}{m L}\right) }{400 \mu L}$
C) $\frac{(400 \mu \mathrm{L}) (100 \mu \mathrm{L}) }{\frac{25 \mu \mathrm{g}}{\mathrm{mL}}}$
D) $\frac{\text { (2) }\left(\frac{25 \mu g}{m L}\right) }{400 \mu \mathrm{L}}$