Which of the following holds good for an elementary reaction as shown in the bellow figure ?

A. The rate of disappearance of ‘Y’ is equal to the rate of appearance of ‘Z’
B. The rate of disappearance of ‘Y’ is equal to the rate of disappearance of ‘X’
C. Three times the rate of disappearance of ‘X’ is equal to the rate of appearance of ‘Z’
D. The rate of disappearance of ‘X’ is equal to the rate of appearance of ‘Z’