For the hypothetical metabolic pathway, A $BCDE,$ with the standard free energy changes for each step listed below, which step would you predict would be most highly regulated?

$AB,G^0=0\mathrm{.}5$

$BC,G=-0\mathrm{.}4$

$CD,G=-19\mathrm{.}6$

$DE,G^{**}=-0\mathrm{.}2$