Cytoplasmic extract from the wild type strain of a bacterium has the ability to convert a colorless substrate $(S)$ to a colored product $(P)$ via three colorless intermediates $X, Y$ and $Z$ in that order. Each step of the pathway involves a specific enzyme coded by a distinct gene. Four mutant strains $(a^- , b^-, c^-, d^-)$ were isolated, whose extracts are incapable of producing the colored product in the presence of $S$. In a series of experiments, extracts from the individual mutants were incubated with $X, Y$ or $Z$ and scored for color development. The data are summarized in the table below. (Yes: color developed, No: no color developed)
Based on the data, which one of the following is the correct order of enzymes involved in the pathway?