If a pipe A can empty a full tank in x hours and two pipes C & D can fill the tank in y hours and z hours respectively then the part of tank filled in 1 hour, when all the pipes are opened together, is _________.

$\frac{xy+xy-yz}{xyz}$ $\frac{yz+zx-xy}{xyz}$ $\frac{zy+xy-zx}{xyz}$ $\frac{xy+yz+zx}{xyz}$

$\frac{xy+xy-yz}{xyz}$