ANSWER
The length of EF is

Step-by-step explanation
The given triangle is a right angle triangle.
The hypotenuse is |ED|. The two shorter legs are |EF| and |DF|.
We can apply the Pythagoras Theorem to find the length of EF.
According to the Pythagoras Theorem,

We now substitute the values in to the formula to obtain,

This gives us,

We now group like terms to obtain,

The right hand side will evaluate to,

We take the positive square root of both sides to obtain,


The correct answer is C.