Which Step Is Catalyzed by the Enzyme Responsible for the Met

Which step is catalyzed by the enzyme responsible for the Met 2 mutant? $\begin{array} { l } \text { Growth Medium }\\\hline \begin{array} { l } \text { Mutant }\\ \text {strain }\\\end{array}&\begin{array} { l } \text { Minimal}\\ \text { medium}\\\end{array}&\begin{array} { l } \text { Minimal+}\\ \text {cysteine }\\\end{array}&\begin{array} { l } \text { Minimal+}\\ \text {cystathionine }\\\end{array}&\begin{array} { l } \text {Minimal+ }\\ \text {homocysteine }\\\end{array}&\begin{array} { l } \text { Minimal+}\\ \text { methionine}\\\end{array}&\begin{array} { l } \text { Compound}\\ \text { accumulating}\\ \text { in mutant}\\\end{array}\\\hline\begin{array} { l } \text { Control}\\ \text {prototroph }\\\end{array}&+&+&+&+&+& \text {None }\\\text { Met } 1&-&-&-&-&+&\text { Homocysteine }\\\text { Met } 2&-&-&-&+&+&\text { Cystathionine }\\\text { Met } 3&-&-&+&+&+&\text { Cysteine }\\\text { Met } 4&-&+&+&+&+&\text { Homoserine }\\\end{array}$

A) homocysteine ?methionine
B) methionine ?homoserine
C) homoserine ?cysteine
D) cysteine ?cystathionine
E) cystathionine ?homocysteine