please help

If the 3f isn't under the radical in the original expression, then it's C. 

You just take the 4 out from under the radical.  It should be +2 though. 

As follows:

$\sqrt{\frac{4e}{3f}}=\sqrt{\frac{4\times3ef}{9f^2}}=\frac{2}{3f}\sqrt{3ef}\\ \text{or just }\frac{2\sqrt{3ef}}{3f}$