\textbf{208--} In a gas-phase reaction, starting at 4 minutes, the change in concentration of substance $A$ equals $0.2$ mol per liter, and the change in concentration of substance $D$ equals $0.17$ mol per liter. If the average rate of change in concentration of substance $X$ is $0.2$ mol per liter per unit time, and in this time interval the closest to the stoichiometric coefficients in the balanced equation, from largest to smallest, to which substances does it correspond?
(1) $X,\ A$ \quad (2) $A,\ X$ \quad (3) $X,\ D$ \quad (4) $D,\ A$
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