When copper is treated with a certain concentration of nitric acid, nitric oxide and nitrogen dioxide are liberated in equal volumes according to the equation
`xCu+yHNO_(3)rarrCu(NO_(3))_(2)+NO+NO_(2)+H_(2)O`
The coefficients `x` and `y` are
A. 2 and 6
B. 4 and 12
C. 1 and 3
D. 3 and 8