Answer:
ZBWCYAX
Explanation:
Equation for the intermediates: Z↔W↔Y↔X
1) B catalyzes the breakdown of Z, therefore inhibiting B leads to the build up of Z.
2) If enzyme C is inactive then the organism will not receive Y to grow, thus Y is a by-product of C.
3) If A is inhibited then W, Y and Z build except for X, thus it make sense that A catalyzes a reaction that leads to X as a by-product.
4) Inhibiting C leads to the reaction toward making Z and W, thus it catalyzes the breakdown of C directly and Z indirectly.