(N/A) The given reaction is: $2H_{2(g)} + CO_{(g)} \rightleftharpoons CH_3OH_{(g)}$
$(a)$ Addition of $H_2$: $H_2$ is a reactant. According to Le Chatelier's principle,adding a reactant shifts the equilibrium in the forward direction to consume the added $H_2$,resulting in an increase in the yield of $CH_3OH$.
$(b)$ Addition of $CH_3OH$: $CH_3OH$ is a product. Adding a product shifts the equilibrium in the reverse direction to consume the added $CH_3OH$.
$(c)$ Removal of $CO$: $CO$ is a reactant. Removing a reactant shifts the equilibrium in the reverse direction to produce more $CO$,resulting in a decrease in the amount of $CH_3OH$.
$(d)$ Removal of $CH_3OH$: $CH_3OH$ is a product. Removing a product shifts the equilibrium in the forward direction to produce more $CH_3OH$.