\[{{\left( \frac{{{a}^{x}}}{{{a}^{y}}} \right)}^{z}}\times {{\left( \frac{{{a}^{y}}}{{{a}^{z}}} \right)}^{x}}\times {{\left( \frac{{{a}^{z}}}{{{a}^{x}}} \right)}^{y}}=\]__________. \[\left( a\ne 0\,\mathbf{and}\,\mathbf{a}\ne 1 \right)\])

• A.  1    
• B.  0             
• C.  \[{{a}^{xyz}}\]                      
• D.  \[{{a}^{xy+yz+zx}}\]