Wiemy, że:

$0<y<x$  

Zatem: 

$\text{|}\underset{x>y}{\underbrace{x-y}}\text{|}+\text{|}\underset{y<x}{\underbrace{y-x}}\text{|}=x-y+\left(x-y\right)=x-y+x-y=2x-2y$  

Odpowiedź: C